Former Maryland Gov. Larry Hogan (R) is running for Maryland’s open U.S. Senate seat, shaking up what was expected to be a breezy general-election contest for Democrats in a deep blue state.

The two-term governor opted to join the fray on Friday, the deadline to file paperwork to replace retiring Democrat Ben Cardin.

The move solidifies that Hogan, a vocal critic of Republican presidential front-runner Donald Trump, will almost certainly not seek to run for president on No Labels’ third-party ticket. But Hogan’s party affiliation means he will be a steep underdog in the Senate race, even if he’s the only candidate on either side who has previously held statewide office.

Hogan, who was term-limited out of the governor’s position in 2022, was the last Republican elected statewide in Maryland, where Democrats now control the governor’s mansion and both legislative chambers. Hogan’s successor, Democrat Wes Moore, won 64% of the vote in 2022 against a hard-right Republican, Dan Cox.

Hogan opened his announcement video with a callback to his father, the late Rep. Larry Hogan Sr. (R-Md.), who voted to impeach President Richard Nixon in 1974.

“Washington is completely broken because that kind of leadership, that kind of willingness to put country over party, has become far too rare,” Hogan said in the video. “My fellow Marylanders, you know me. For eight years, we proved that the toxic politics that divide our nation need not divide our state.”

Hogan, 67, did not mention Trump in his video, but he’s known for opposing the former president. In a March 2023 New York Times op-ed, Hogan argued it was time for Republicans to ditch Trump. “We cannot afford to have Mr. Trump as our nominee and suffer defeat for the fourth consecutive election cycle,” he wrote.

Still, it’s not clear that there’s a path to the Senate, or a place in it, for a Republican who is also a Trump antagonist ― especially with Trump expected to easily win the GOP presidential nomination. The Senate’s most vocal Republican critic of Trump, Utah’s Mitt Romney, is retiring at the end of 2024, opening up an opportunity for a Trumpier Republican in that state and potentially leaving behind a dearth of anti-Trump conservatives in the upper chamber.

Hogan’s announcement Friday hit on the ubiquitous campaign theme of curing Washington gridlock. “The politicians in Washington seem to be more interested in arguing than in actually getting anything done,” he said in his video.

Hogan doesn’t face major opposition in the GOP primary, but his entry sets up an expensive general-election battle for Cardin’s seat.

In the Democratic primary, Rep. David Trone, the owner of Total Wine & More, has already spent more than $23 million in the race against Prince George’s County executive Angela Alsobrooks, who has managed to consolidate institutional Democratic support. Hogan’s entry means that Trone and national Democrats may have to spend millions more to keep the seat in Democratic hands.

“Larry Hogan’s candidacy is nothing but a desperate attempt to return Mitch McConnell and Donald Trump to power and give them the deciding vote to ban abortion nationwide, suppress votes across the country, and give massive tax cuts to the wealthiest Americans,” Trone said in a statement that suggests Democrats intend to hit Hogan hard on the abortion issue in a blue state.

Hogan is running in the May 14 GOP primary against former Maryland Del. Robin Ficker and nurse Lori Friend.