June 1, 2026, 5:00 AM EDTFour House incumbents have already lost re-election bids so far this year, just a few months into primary season. And about a dozen more are facing legitimate threats in the coming months.Two Republican incumbents are squaring off for one district in California next week, the latest example of redistricting changing not just general elections but primaries as well, after two Democratic members lost in Texas last week. 01:43But the heaviest upcoming primary action will be on the Democratic side. A handful of Democratic incumbents in California will also face energetic challengers arguing that voters want a fresh face, part of a national slate of anti-incumbent candidates focused on generational change. A wealthy incumbent Democrat in Maryland is running against an even wealthier former congressman in a primary there.And other Democrats in states like Colorado and Massachusetts face challenges from their party’s left flank, part of a running battle between progressives and the Democratic establishment. The incumbent primary danger stretches from Connecticut and New York to California and beyond: Hawaii’s oldest member of Congress is fighting for his political survival, too, from a challenger backed by a former governor. Incumbent members of Congress are notoriously difficult to defeat. But many Democrats are facing stronger challenges this election cycle than ever before, as party members look to turn the page on the 2024 presidential election and mount an effort to retake control of Congress. In California, that’s led to legitimate Democratic challengers popping up in the state’s top-two, all-party primaries against Reps. Mike Thompson, Doris Matsui, Brad Sherman, Jimmy Gomez and Linda Sánchez. Many of these are generational challenges, with younger Democrats calling on voters to move on from entrenched incumbents. Some are better funded than others: Thompson’s challenger, entrepreneur Eric Jones, has given more than $5 million to his own campaign, while former White House policy aide Jake Levine loaned his campaign $500,000 to help him narrowly outraise Sherman.And some of the longtime incumbents are sounding the alarm in ways that suggest they could face real political danger. Matsui’s campaign website includes a message to outside groups asking them to boost a Republican candidate — a move that could help block Democrat Mai Vang, a member of the Sacramento City Council, from advancing to a general election matchup against Matsui. Seeking generational changeAfter California’s all-party primaries Tuesday, more traditional party contests lie in wait.Like some of their California colleagues, Democratic Reps. Stephen Lynch of Massachusetts, John Larson of Connecticut, Ed Case of Hawaii, Diana DeGette of Colorado, Shri Thanedar of Michigan and Adriano Espaillat of New York are facing challenges from much younger Democrats calling for a new approach and a fresh face. Larson’s challenger, former Hartford Mayor Luke Bronin, is one of those candidates. He’s outraised the longtime congressman and won the state Democratic Party endorsement at its convention.Larson, a former member of House Democratic leadership who serves on the important House Ways and Means Committee, has brushed aside the vote, arguing the will of the party delegates doesn’t reflect broader voter opinions. The incumbent says his experience is an asset for Connecticut and a freshman replacement would need to climb the ladder slowly before gaining his influence in Washington. “I don’t know what Luke stands for, other than I’m old,” Larson said on a press call last week flanked by allies from the Working Families Party and others, where he said he’s running for re-election in part to champion his push to strengthen Social Security.He claimed that Bronin, a previous supporter, met him before launching his campaign and told the incumbent to step aside. “He told me he was going to turn me into Joe Biden, and I was in for a tough slog,” Larson added. “And I told him: ‘You don’t know me.’”Bronin denied making either pronouncement, telling NBC News that “the conversation John now recounts has almost no resemblance to the conversation that actually happened.”“The fact that John is now saying that he found it laughable that someone would suggest that after 28 years in Congress, maybe it was time to pass the torch, reveals a kind of mind-blowing sense of entitlement that is part of the problem,” he said. “Congressional seats were not meant to be lifetime appointments and the Democratic Party would be so much stronger if we had more people who recognize that part of leadership is knowing when it’s time to pass the torch,” Bronin added.The left versus the establishmentOther Democratic primaries are strictly playing out more as battles between progressives and moderates — though some of the generational primaries have at least a sprinkling, if not a heaping helping, of ideological divides layered on top of questions about age. Justice Democrats, a progressive group that has backed anti-incumbent primary challengers like Rep. Alexandria Ocasio-Cortez, has endorsed a slate of 2026 challengers that includes Colorado lawyer Melot Kiros, who is running against DeGette. The group is also behind Vang’s bid against Matsui in California; activist Darializa Avila Chevalier’s bid against Espaillat in New York; state Rep. Donavan McKinney’s bid against Thanedar in Michigan; and former Rep. Cori Bush’s comeback bid in Missouri against Rep. Wesley Bell. Our Revolution, a group born out of Sen. Bernie Sanders’ 2016 presidential bid, has endorsed an overlapping group of candidates including Avila Chevalier, Vang and Bush. The group is also backing Levine against Sherman and Jones against Thompson in California, as well as former New York City Comptroller Brad Lander’s campaign against Rep. Dan Goldman in New York. And New York City Mayor Zohran Mamdani, riding the political high of his first year in office following 2025 primary and general election victories over former Gov. Andrew Cuomo, is supporting Lander and Avila Chevalier in their primary challenges, too.A heated Republican race, tooMeanwhile, some of the primary challenges on the Democratic side defy easy characterization. That’s especially true in Maryland, where Rep. April McClain Delaney is running for re-election against former Rep. David Trone, who vacated this seat for an unsuccessful Senate bid last cycle.Both candidates are independently wealthy and have leaned on their personal fortunes, though Trone’s $10 million investment in his campaign dwarfs Delaney’s $2 million. That race has gotten heated, too, with Trone hammering Delaney for past immigration votes like her support of the Laken Riley Act, and Delaney pushing back by trying to tie Trone to Republicans by looking at past donations.However intense the Democratic contests may be, the most heated incumbent primary of them all right now might be between California Republican Reps. Ken Calvert and Young Kim, who are running against each other in a brutal campaign prompted by state Democrats’ redistricting efforts. After years of trying to distance herself from Trump while running in more moderate districts, Kim has rebranded herself a “100%” supporter of Trump. Calvert has hammered her for that shift — and gone as far as claiming her past criticism of Trump stoked the environment that led to the recent assassination attempt against him and top Cabinet officials at the White House Correspondents’ Association dinner.Kim has argued it’s time for Calvert to pass the torch, and more recently, she started running ads noting an early ’90s incident in which Calvert, then a freshman congressman, was caught engaged in a sex act in a car with a woman whom local police had identified as a known prostitute, according to a contemporaneous report in the Los Angeles Times.Both Calvert and Kim are well liked among House Republicans, with Calvert chairing a key subcommittee and Kim earning praise for holding on to an Orange County seat in tough conditions in recent years.“Republicans are going to lose a great member one way or the other in this district,” said Dave Gilliard, a longtime California Republican strategist who isn’t working in the race. “When the stakes are this high, and careers are on the line, it’s to be expected the rhetoric will get hotter and hotter and hotter,” Gilliard said.