With Election Day six months away, senators facing well-funded challengers from their own parties and the late entry of a game-changing candidate have shaken up CQ Roll Call’s list of the 10 most vulnerable Senate incumbents.

Both appointed Georgia Republican Kelly Loeffler and Massachusetts Democrat Edward J. Markey make the list because of challenges from House colleagues. Montana GOP Sen. Steve Daines joins them because Democratic Gov. Steve Bullock jumped into the race after a failed presidential run.

With the new additions, Republicans David Perdue of Georgia and John Cornyn of Texas fall off the list, along with New Hampshire Democrat Jeanne Shaheen. Perdue and Cornyn could still face competitive reelections. Inside Elections with Nathan L. Gonzales rates both races Likely Republican, but moved the New Hampshire race to Solid Democratic earlier this month.

Seven of the 10 most vulnerable senators are Republicans, no surprise with the GOP defending 23 seats this year to 12 for the Democrats. Democrats need a net gain of four seats to retake the Senate, or three if they win the White House since the vice president would be the tiebreaking vote. Recent fundraising numbers have boosted their prospects, with a slew of challengers outraising GOP incumbents in the first quarter of 2020. 

[See October updates to lists of most vulnerable House members and senators]

All candidates face an uncertain political environment as the coronavirus pandemic unfolds, and as the race between President Donald Trump and former Vice President Joe Biden, the presumptive Democratic nominee, heats up.

The 2016 presidential results in these states were factored into the rankings, along with conversations with strategists on both sides of the aisle and race ratings from Inside Elections.

Jones won a low-turnout special election in 2017 against a deeply flawed GOP candidate, former Alabama Supreme Court Chief Justice Roy Moore. Moore’s attempted comeback ended in a fourth-place finish in the March 3 primary. Former Attorney General Jeff Sessions, who gave up this Senate seat to lead the Justice Department, and former Auburn football coach Tommy Tuberville, who has Trump’s endorsement, are in a runoff that was delayed from March 31 to July 14. A prolonged and divisive GOP primary could help Jones. He had $8.3 million in the bank on March 31, while Sessions had $749,000 and Tuberville $456,000. But that financial edge might not be enough in deep-red Alabama.

As one of two GOP senators running in a state that Hillary Clinton won in 2016, Gardner started the 2020 cycle as one of the most vulnerable incumbents. And he remains in the second spot on this list because of that dynamic and because he could face former Colorado Democratic Gov. John Hickenlooper, who made an unsuccessful run for president before deciding to run for Senate. Hickenlooper, who has been endorsed by the Democratic Senatorial Campaign Committee, still has to win a June 30 primary. But he has proved to be a strong fundraiser, outraising Gardner in the first quarter. Gardner still had more cash on March 31, with $9.6 million to Hickenlooper’s $4.9 million.

McSally’s Democratic opponent, Navy veteran and retired astronaut Mark Kelly, has outraised her for five consecutive quarters. Kelly, who is married to former Democratic Rep. Gabrielle Giffords, also had more cash on hand, with $19.7 million to McSally’s $10.2 million on March 31. Democrats are continuing to attack McSally’s health care record, recycling similar attacks the retired Air Force pilot faced during her unsuccessful run for Senate two years ago. McSally was appointed to the late Sen. John McCain’s seat after she lost that 2018 race to Democrat Kyrsten Sinema. The 2020 race is for the final two years of McCain’s term.

In a sign Republicans knew Tillis needed help, a GOP super PAC, the Senate Leadership Fund, spent more than $2.5 million — through yet another outside group — to promote a more liberal candidate in this year’s Democratic primary. The goal was to force the front-runner, ultimate nominee Cal Cunningham, and his supporters to spend their money earlier than they otherwise would have. Tillis has taken a moderate tone to campaigning amid the pandemic, including running an ad touting his bipartisan work on relief legislation. Cunningham, an Army veteran and former state senator, raised more money in the first quarter, but Tillis had $6.5 million on hand on March 31 to the Democrat’s $3 million.

It’s hard to overstate how much Collins’ political fortunes have changed as she has sought to navigate the volatile Trump era while preserving her reputation as an independent-minded moderate. She voted to acquit the president on impeachment charges and cast a pivotal confirmation vote in 2018 to put Brett M. Kavanaugh on the Supreme Court amid allegations of a long-ago sexual assault. Such votes helped fuel fundraising by her most likely opponent, Democrat Sara Gideon, the state House speaker, who outraised Collins in the first quarter. Collins still had more cash on hand, $5.6 million to Gideon’s $4.6 million on March 31. Outside groups are lining up to spend big in the state.

Loeffler’s campaign has been reeling since the March revelation that she sold $20 million in stocks after attending a closed-door coronavirus briefing. She has tried to control the damage, but the scandal could boost GOP Rep. Doug Collins in the November special election in which candidates from all parties run on the same ballot. Loeffler was appointed to the vacant seat by Gov. Brian Kemp despite Trump’s preference for Collins. Both were outraised in the first quarter by Democrat Raphael Warnock, but Loeffler has significant personal wealth, and the National Republican Senatorial Committee continues to support her. With more than 20 candidates in the race and none likely to clear 50 percent, Loeffler would need a top-two finish to make a January runoff.

Republicans, who are mostly on defense under the 2020 Senate map, have targeted Peters because he’s in a battleground state where Trump eked out a victory four years ago. Peters has responded with record-setting fundraising, though his presumed opponent, GOP Army veteran John James, has continued to best him in quarterly fundraising hauls. James lost a 2018 race to Sen. Debbie Stabenow by 7 points. Peters had $8.8 million on hand to James’ $8.6 million on March 31. But James has collected more money, $5.2 million, from donors giving less than $200. His fundraising strength speaks, in part, to Republicans’ scant opportunities for Senate pickups this year.

Unlike some Republicans who’ve known for months they were at risk, Daines became vulnerable in March when Bullock threw his hat in. Then the pandemic disrupted campaigning, and Bullock remained in the spotlight, directing his state’s response as governor. That could help — or hurt — him in November. The GOP’s also going to use comments he made during his unsuccessful bid for the presidency, including his support for an assault rifle ban and saying that Washington “is captured by dark money” on gun policy, climate change and prescription drug costs. Bullock’s $3.2 million on March 31 trailed Daines’ $5.6 million. But Bullock raised it in a matter of weeks.

Super PACs are preparing to spend millions in Iowa, underscoring that Ernst’s reelection is a top contest. Ernst is still considered popular in the state, where she does an annual 99-county tour. But Democrats are looking to paint her as a partisan politician who no longer prioritizes the Hawkeye State. The DSCC has endorsed real estate executive Theresa Greenfield, who has been stressing her rural roots and pledging to protect programs including Medicare and Social Security. Greenfield had $3.8 million on March 31, but she still has to win a June 2 primary. Ernst had $6.5 million and faces no primary opposition.

Markey would be a shoo-in against practically any Republican, but a challenge within his own party from Rep. Joseph P. Kennedy III is potentially insurmountable. The real election is the Sept. 1 primary. The incumbent senator and the congressman from a political dynasty with deep Massachusetts roots have few policy differences, but Kennedy has been ahead in polling and fundraising. He had $6.2 million on hand as of March 31 to $4.4 million for Markey. It’s also a generational fight. Markey, at 73, served 18 terms in the House before moving up to the Senate seven years ago. Kennedy, who turns 40 in October, is in his fourth House term.