Montana Gov. Steve Bullock announced Monday that he will run for Senate, in a reversal that boosts Democrats’ fortunes in their bid to unseat Sen. Steve Daines (R-Mont.) and reclaim the Senate majority.

Republicans hold 53 seats in the chamber, and the popular Bullock’s entry into the Montana race would increase Democrats’ chances of picking up the four GOP seats they would need to reclaim control.

In a statement, Bullock said that after speaking with his family, he decided to enter the race “so we can make Washington work more like Montana.”

“As governor, I’ve worked my level best to represent all Montanans and leave this place we call home better than I found it, and in a time when our politics is more divided than ever, we’ve been able to accomplish a great deal for the people of our state,” Bullock said.

“We can’t say the same about Washington, where they can’t tackle the difficult challenges like health care costs, climate change and a changing economy or even the ones we agree on like strengthening our infrastructure, lowering drug prices and banning dark money from our federal elections,” he added.

Democrats’ best opportunities to unseat Republican senators are in Arizona, Colorado, Maine, North Carolina and Iowa, while the GOP is looking to flip the Alabama seat held by Sen. Doug Jones (D).

Colorado and Maine are Democratic-leaning states that backed Hillary Clinton in 2016, making Sens. Cory Gardner and Susan Collins increasingly vulnerable. In Arizona, appointed Sen. Martha McSally (R) faces a tough challenge from former astronaut Mark Kelly.

Sens. Thom Tillis (R-N.C.) and Joni Ernst (R-Iowa) have faced diminishing support as Democrats rally around their opponents.

The election will test the power of incumbency and whether President Trump at the top of the ticket is beneficial.

News of Bullock’s decision was first reported last week by the New York Times. The governor’s announcement Monday came hours ahead of the state’s filing deadline.

According to a person familiar with Bullock’s thinking, who spoke on the condition of anonymity to discuss internal deliberations, the governor’s decision came in the past week or two, when his wife and three children switched their longtime opposition to him running for Senate and urged him to jump into the race.

Bullock dropped out of the Democratic presidential primary in December, noting in a statement that he “won’t be able to break through to the top tier of this still-crowded field.”

The Montana Democrat, who is term-limited as governor, had pitched himself to voters as a moderate outsider and campaign-finance reformer who would be able to beat Trump in red states. But his campaign struggled to gain traction, and he qualified for only one of the Democratic debates.

Both before and after his presidential bid, Bullock rejected pleas from national Democrats to run for Senate and repeatedly told reporters he was not interested in the job.

Yet Democratic leaders continued to keep their eye on him, and Senate Minority Leader Charles E. Schumer (D-N.Y.) flew to Montana late last month to lobby Bullock to run, Politico reported.

Former president Barack Obama also encouraged Bullock to run during a meeting in Washington earlier this year, according to Politico.

Two national Republican groups have in recent days previewed the attacks the GOP will make against Bullock.

The Senate Leadership Fund, a top Republican super PAC, on Monday took aim at Bullock over his failure to alert New York Mayor Bill de Blasio’s office about an aide he had fired in 2015 over sexual harassment allegations.

The aide went on to allegedly harass at least two other women while working for de Blasio (D), who also fired him. Bullock has apologized and said he “should have reached out” to de Blasio to warn him.

“Steve Bullock’s history of failing to protect women in the workplace is shameful and wrong,” SLF communications director Jack Pandol said in a statement. “A person with Bullock’s poor judgment has no business serving in the United States Senate representing Montana, and we are confident once voters learn about the real Steve Bullock, they’ll agree wholeheartedly.”

In a statement last week, the National Republican Senatorial Committee also cited the incident, as well as Bullock’s embrace last year of an assault weapons ban and his support for impeaching Trump.

“Succumbing to overtures from national Democrats like Chuck Schumer and Barack Obama, Steve Bullock is giving a foolish senate run another look,” NRSC spokesman Nathan Brand said. “Whether it’s his support for removing President Trump from office, banning guns, or allowing a top staffer to prey on women, Bullock lacks the character and values Montanans expect from a senator.”

Mike DeBonis contributed to this report.