A growing list of House Democrats from competitive districts is headed for the exits, adding yet another concern for a party facing an uphill fight to maintain control of Congress next year.

The latest to announce her departure is Rep. Cheri Bustos (D-Ill.), the former head of the Democratic Congressional Campaign Committee, who proclaimed her coming retirement Friday after narrowly winning reelection in a rural district along the Mississippi River that supported former president Donald Trump.

Rep. Charlie Crist (D-Fla.), who has been exploring another possible gubernatorial run, put out word Saturday that he would be making a “major announcement” this week, potentially putting at risk his St. Petersburg seat, where he ran ahead of President Biden in 2020.

Two other accomplished battleground incumbents — Reps. Filemon Vela Jr. (D-Tex.) and Ann Kirkpatrick (D-Ariz.) — announced their plans to leave earlier this year, joining Rep. Tim Ryan (D-Ohio), who is giving up a closely contested seat to run for the U.S. Senate. Several more in competitive areas, including Democratic stars like Reps. Conor Lamb (Pa.) and Stephanie Murphy (Fla.) are also seriously considering runs for higher office later this year.

The exodus comes as the party struggles to maintain or extend the narrowest congressional majority in decades — six seats, which will grow to seven in coming days as a newly elected Democrat, Troy Carter from Louisiana, is sworn in.

Democrats have little margin for error to keep control, even as they simultaneously will be working against a redistricting cycle that is likely to favor Republican officeholders.

The Democratic departures are likely to make it easier for sometimes-partisan mapmakers to draw maps that favor Republican pickups. They also mean that Democrats will not fully take advantage of incumbency, with its fundraising and name recognition benefits. In 2018, the last midterm shake-up, 91 percent of incumbents won reelection, according to the Center for Responsive Politics.

This time, Democrats will be the ones fighting historical head winds that tend to punish the president’s party in midterm elections. Since 1910, the party in the White House has gained House seats in a midterm only three times: in 1934, after the election of President Franklin Delano Roosevelt; in 1998, during President Bill Clinton’s second term; and in 2002, when President George W. Bush was leading a response to the terrorist attacks of Sept. 11, 2001. Clinton lost 54 seats in his first midterm. President Barack Obama lost 64. Trump gave up about 40.

Amid these grim odds, retirements have long been viewed by party strategists as a key early metric of just how challenging an election cycle will be. Similar early decisions to leave Congress have been a bane for Republicans in recent midterms, playing a major role in the 2018 Democratic takeover of the House, which followed an exodus of 33 GOP members — nearly twice as many as Democrats.

“In 2018, there is no doubt that Republican retirements and late redrawing of maps made a significant difference in our ability to win additional seats,” said Dan Sena, the DCCC’s executive director that cycle.

Now those advantages are more likely to go to Republicans. Only one Republican from a competitive seat, Rep. Lee Zeldin (N.Y.), has signaled so far that he will leave the House to run for governor. The other three announced GOP retirements hail from safe Republican districts. (Three additional Democratic seats are vacant with special elections to fill them planned for this year.)

“The tables have turned. Republicans are on offense,” said National Republican Congressional Committee spokesman Michael McAdams. “A lot of these vulnerable Democrats are in swing districts and are going to have to contend with new district lines, and they want to get off House Democrats’ sinking ship.”

Democratic strategists are betting that the infighting in the Republican Party, the extremism on display during the Jan. 6 attack on the U.S. Capitol and the sheer scale of the trillion dollar programs Democrats have pushed through this year will lead to a reorienting of partisan divisions that can overcome historical patterns. They also argue that decisions by Democrats to run for higher office can be seen as a sign of strength, an effort to build on their 2020 victories in a number of competitive Senate contests and the 36 states where governors will be up for election next year.

“I wouldn’t be surprised if slightly more Democrats in the House are doing it because Democrats have big wins to run on,” said Karen Defilippi, the DCCC’s deputy executive director for campaigns. “We just passed critical covid-19 relief that put shots in arms, cash in pockets, funding that safely reopens schools and gets workers back on the job.”

On the Senate side, where both parties control 50 seats, the retirement burden is expected to fall more heavily on Republicans this cycle, with five members of the party already having announced their retirements. They include Sens. Patrick J. Toomey (R-Pa.), Rob Portman (R-Ohio) and Richard Burr (R-N.C.), whose seats could all provide pickup opportunities for Democrats. Another Republican up for reelection, Sen. Ron Johnson of Wisconsin, a state that Biden won, has not yet said whether he is running for reelection.

The House is more challenging for Democrats because of Republican control over the redistricting process in key states like Florida and Texas, which will both add congressional seats this year, leading to a redrawing of lines to benefit the party. Illinois, Pennsylvania and Ohio will all give up congressional representation, forcing a similar, though less partisan, reshuffling of district boundaries.

If Crist does announce a run for governor, he will making his seventh statewide bid for office in Florida, his second attempt as a Democrat for governor. He won three times as a Republican, becoming education commissioner, attorney general and then governor between 2006 and 2010. He subsequently lost a bid for Senate in 2010 and a Democratic campaign for governor in 2014, falling to then-Gov. Rick Scott (R) by a single percentage point.

At least two Democratic members of Congress from Florida have already suggested they are likely to join Crist in seeking higher office later this year. Rep. Val Demings, who represents a safe Democratic seat in Orlando, has said she is looking at running for either governor or U.S. Senate. Murphy, who knocked out the powerful Rep. John L. Mica (R-Fla.) in 2016, has said she is “seriously considering” a Senate bid.

A similar situation is developing in Pennsylvania, where the open Senate seat has attracted the early interest of Lamb, one of the most celebrated Democratic moderate candidates in recent years, and Rep. Chrissy Houlahan (D-Pa.), who holds a Democratic-leaning district in the outskirts of Philadelphia. (Rep. Dan Meuser (R-Pa.) has been considering his own gubernatorial run.)

Beyond that list, the discussion becomes far more speculative. Democrats have been urging Rep. Vicente Gonzalez Jr. (Tex.) to stay in Congress, after his neighboring Democrat, Vela, decided to call it quits. In a move Republicans see as a hopeful sign that he may soon depart, Gonzalez recently paid off a $250,000 personal loan he had given his campaign.

The decision by Bustos to move on, after leading House Democrats through the 2020 cycle, is particularly symbolic. She authored a 2018 report for the party aimed at expanding the reach of Democrats among rural working class White voters who had lifted Trump to victory in 2016.

Yet Trump doubled his margin of victory in her working class district in 2020 against Biden, compared with his 2016 performance against then-Democratic nominee Hillary Clinton.

“As a Democratic Party leader, she’s modeled what it means to build our party at the grass roots level,” current DCCC chairman Sean Patrick Maloney (D-N.Y.) said after she announced her intention to retire.

Correction: An earlier version of this story misstated the number of statewide races Rep. Charlie Crist (D-Fla.) has run. He has run seven times, not six, including a 2010 campaign for U.S. Senate, when he dropped out of the Republican primaries to run as an independent. It also misstated the number of times the president’s party has won seats in a midterm since 1910; it is three times, not two.