Rep. Gosar under fire for anime attacking Rep. Ocasio-Cortez

Incumbent: Republican Pat Toomey (retiring)

The biggest development in the Keystone State, which remains the seat most likely to flip partisan control, was Trump earlier this month wading into the GOP primary to replace retiring Sen. Pat Toomey. He backed Army veteran Sean Parnell, who lost a 2020 House bid to Democratic Rep. Conor Lamb (who's running for the Democratic nod for this seat). Parnell already had support from the former President's son, Donald Trump Jr., so getting the elder Trump's backing wasn't a big surprise. But rather than doing anything to clear the field, the endorsement may be making this race more ugly, with businessman Jeff Bartos launching personal attacks on Parnell. Democrats are happy to see Republicans go after each other, while they attack the GOP on issues ranging from partisan audits to abortion restrictions. Montgomery County Commissioner Val Arkoosh, for example, who's running with the backing of EMILY's List and 314 Action, has been outspoken about the threat to abortion rights and the importance of the Supreme Court. "A woman physician has never served in the U.S. Senate before -- ever," she wrote in a recent op-ed touting her science background. Republicans, however, think a national environment that looks worse for Biden could help them hold onto this seat, especially with the biggest fundraiser in the race pushing the party to the left on some issues. "Stop apologizing for the space we take up as a party and ram some stuff through and get it done," Pennsylvania Lt. Gov. John Fetterman told CNN in a recent interview about his strong belief in eliminating the filibuster. That's just what Republicans want to hear as they look to attack him as too extreme for this purple state. Still, Democrats have the edge in a state that Biden carried in 2020.

Incumbent: Democrat Raphael Warnock

Former football star Herschel Walker, the man who was freezing the Republican field in Georgia for months, finally launched his Senate campaign late last month, which was quickly followed by an unsurprising Trump endorsement. The former President is holding a rally in the Peach State this weekend, where he's sure to share his thoughts on candidates up and down the ballot there as he seeks revenge on Republicans whom he thinks were insufficiently supportive of his efforts to overturn the 2020 election. Agriculture Commissioner Gary Black, who's tried to attack Walker, is still running for the GOP nomination, as are a handful of others. It remains to be seen how much establishment Republicans worried about Walker's candidacy can do about it now that he's in the race with Trump's backing. But Sen. Raphael Warnock, who's running for a full six-year term, is glad to have the Democratic field to himself as he raises money for what's sure to be a hotly competitive general election race, regardless of how the GOP primary shakes out. After winning the presidential contest here, as well as two Senate runoffs that flipped the balance of the chamber, Democrats are hopeful that a competitive governor's race -- and especially a potential Stacey Abrams candidacy -- will help juice turnout in a non-presidential election year.

Incumbent: Republican Ron Johnson

It's the question that no one seems to know the answer to -- except, maybe, the senior senator from Wisconsin himself: Is Ron Johnson running for a third term? At this point, given his penchant for saying controversial things about the 2020 election, the January 6 insurrection, the coronavirus and vaccines, Democrats seem to be just as happy running against the two-term Republican as they would be if he retired and this were an open seat. Only 35% of Wisconsin voters viewed Johnson favorably in a Marquette University Law School poll from mid-August, while 42% viewed him unfavorably. But his lowest net favorability was in November 2015, the year before he came from behind to win a second term. Republicans point to that 2016 election to argue that Johnson, who previously promised to serve only two terms, has been discounted before. While ambitious Republicans wait in the wings to see what Johnson will do, Democrats have a very crowded field. Lt. Gov. Mandela Barnes recently picked up a high-profile progressive endorsement in Massachusetts Sen. Elizabeth Warren.

Incumbent: Democrat Mark Kelly

Nearly a year after Biden won Arizona and Democrat Mark Kelly unseated GOP Sen. Martha McSally, Republicans are still litigating the 2020 election here. Attorney General Mark Brnovich had earned Trump's ire for not doing enough to audit the state's election results, despite there being no evidence of fraud. "Hopefully he's going to do what everybody knows has to be done," Trump said of the attorney general at a late June rally in the state. Since then, Brnovich has leaned into the partisan review pushed by the GOP-led state Senate, threatening to withhold funds from Maricopa County because he alleged the county's supervisors did not fully respond to a subpoena for the so-called audit. And earlier this month, Brnovich announced the state is suing the Biden administration for "federal overreach" over the President's vaccine mandates. Meanwhile, a super PAC supporting Blake Masters, the president of the Thiel Foundation, went up with an ad earlier this month hitting Brnovich for "saying President Trump is wrong on voter fraud" and "making excuses instead of standing with our president." Democrats are happy to have Republicans attacking each other -- and pushing each other to the right -- as Kelly wracks up money. They're hoping that 2020 election denialism, while perhaps an important litmus test in the GOP primary, will be unpalatable to general election voters next November. Republicans, however, contend that issues like immigration will be of far greater importance next fall, which is why they've been attacking Kelly on the border and trying to use fellow Democratic Sen. Kyrsten Sinema as a moderate foil to make him look too liberal.

Incumbent: Republican Richard Burr (retiring)

Trump endorsed in the GOP primary to replace retiring Sen. Richard Burr back in June, throwing his support behind Rep. Ted Budd in a surprise announcement in front of other contenders. But former Gov. Pat McCrory and former Rep. Mark Walker aren't backing down. Meanwhile, the political arm of the Conservative Club for Growth, which has stood by Budd since helping him emerge from a 17-way House primary in 2016, is taking the airwaves to attack McCrory, arguing that he cannot win because he lost reelection in 2016 when Trump won the state. Walker has tried to make a similar argument about McCrory, while both he and McCrory have piled on Budd. Trump carried the Tar Heel State by just over a point in 2020, making this potentially competitive terrain even if Republicans start with the early advantage. State Sen. Jeff Jackson, who's been in the race since January, had raised the most money on the Democratic side by the end of the second quarter. But former state Supreme Court Chief Justice Cheri Beasley, who joined the race in late April, raised $1.3 million during the second quarter. Besides EMILY's List, she has the backing of Higher Heights PAC, which works to elect progressive Black women, and the political arm of the Congressional Black Caucus, reflecting the enthusiasm for a non-White male candidate helping turn out minority voters in a non-presidential year, especially in some of the rural areas where Republicans have continued to hold an advantage.

Incumbent: Democrat Maggie Hassan

As Republicans grow more excited about Gov. Chris Sununu possibly running for Senate, Democrats are finding more reasons to argue that electing a Republican at the federal level in New Hampshire isn't the same as electing one to serve in Concord. They're largely turning to abortion to make that case, highlighting a budget the governor signed that included abortion restrictions and the Executive Council's recent vote to defund Planned Parenthood and family planning providers. (Sununu does not have a vote on the council and called the vote "incredibly disappointing" in a statement.) Despite the state trending blue at the federal level, Republicans are convinced that first-term Sen. Maggie Hassan is highly vulnerable, and both sides admit this race isn't likely to look like 2020, when Sen. Jeanne Shaheen won reelection by nearly 16 points. But Sununu keeps pushing back his timeline for making a decision about running, so, for now, Hassan has the race largely to herself. She released her first TV ad earlier this month -- a positive spot that touches on her father's service in World War II and her own work for veterans. Even if the governor doesn't run, however, Hassan could have a strong challenger in former Sen. Kelly Ayotte, whom the Democrat beat by just over 1,000 votes in 2016.

Incumbent: Democrat Catherine Cortez Masto

Democratic Sen. Catherine Cortez Masto finally has a high-profile opponent in former Nevada Attorney General Adam Laxalt, whom national Republicans had long eyed as the top challenger but who officially launched his campaign at the end of August. He's the rare GOP candidate who was recruited by Senate Minority Leader Mitch McConnell and has Trump's endorsement, making it more likely he'll have the GOP field mostly to himself as other ambitious Republicans jockey for the gubernatorial nomination. As Tump's campaign co-chair in the Silver State, Laxalt followed the former President's lead on false charges of voter fraud, for which Trump praised him in offering his endorsement last month, and he's already made some noise about filing lawsuits in 2022. Democrats are hoping his embrace of Trump's election fraud narrative will help tie him to the former President and turn off voters in a state that Biden carried last fall. His position on abortion could be also be litigated in the general election, especially since Nevada has a history of GOP leaders who have been more supportive of abortion rights, like former GOP Gov. Brian Sandoval. Democrats hope to argue that Laxalt is out of touch with voters on the issue. Still, Biden only carried the Silver State by just over 2 points, and Cortez Masto is running for her first reelection, so Democrats aren't taking anything for granted here, especially with an uncertain post-pandemic electorate.

Incumbent: Republican Marco Rubio

GOP Sen. Marco Rubio starts with the advantage in this state that Trump carried by 3 points last year. But Democratic Rep. Val Demings, who outraised Rubio in the second quarter, is proving to be a strong fundraiser who could give the Republican senator a real race. Rubio is trying to tie Demings to "the socialist squad" and Democrats' physical and human infrastructure bills. (Rubio voted against the bipartisan $1 trillion infrastructure bill in the Senate last month.) Demings has attacked Rubio for traveling to Iowa late last month while Florida is dealing with the Delta variant surge.

Incumbent: Republican Rob Portman (retiring)

GOP Sen. Rob Portman's decision to retire has opened up a crowded GOP primary, with most contenders trying to "outTrump" each other in a state the former President won by 8 points. State Sen. Matt Dolan, who entered the race this week, cuts a more moderate profile. He supports the bipartisan infrastructure bill that Portman negotiated, according to an interview with Cleveland.com, and has been critical of Trump's election lies. But it's unclear how much traction he can get in a GOP primary where the former President's influence is king with the base. Trump already attacked Dolan, whose family owns Cleveland's baseball team, for "cancel culture" because they decided to change the team's name. Former state treasurer Josh Mandel has been courting that conservative base hard, attacking refugees despite his own family history. JD Vance, the author of "Hillbilly Elegy," has been leading in earned media attention and is wracking up endorsements from conservative leaders like Missouri Sen. Josh Hawley and Indiana Rep. Jim Banks, the chair of the largest conservative caucus in the House. Those endorsements could help compensate for his prior criticism of Trump, which his opponents are eager to use against him. Former state party chair Jane Timken, businessmen Mike Gibbons and Bernie Moreno are also running. On the Democratic side, Rep. Tim Ryan recently got a challenge from his left in Morgan Harper, who's arguing that she can drive the minority turnout needed to turn Ohio blue. Harper lost a 2020 primary challenge to Rep. Joyce Beatty, who's now the chair of the Congressional Black Caucus and has backed Ryan.

Incumbent: Republican Roy Blunt (retiring)

Missouri continues to occupy the 10th spot on this list because of the chance that the Republican nominee to replace retiring Sen. Roy Blunt will give Democrats an opening. But it would be a massively uphill climb for Democrats to flip this seat blue in a state that Trump won by 15 points. Their best hope is former Gov. Eric Greitens, who resigned from office following a probe into allegations of sexual and campaign misconduct, winning the GOP nomination and creating a Todd Akin situation. The 2012 Senate nominee's "legitimate rape" comments cost Republicans the Missouri Senate seat and imperiled GOP nominees across the country. Greitens, who has been picking up endorsements from Trump world -- recently former national security adviser Michael Flynn, for example -- hardly has the field to himself. Attorney General Eric Schmitt is running, with his super PAC allies leaning into his suit against mask mandates in schools to tout his candidacy. Reps. Billy Long and Vicky Hartzler are also running, as is Mark McCloskey, whom the Republican governor pardoned last month after he and his wife had pleaded guilty to misdemeanor charges for pointing guns at protesters near their home last summer. While GOP voters will have plenty of candidates to choose from, more candidates means a more splintered vote, which could lower the threshold it takes for Greitens to win the nomination.