A Texas Democrat hasn’t had a seat in the U.S. Senate since 1993, but U.S. Rep. Beto O’Rourke is hoping to change that. The representative of the state’s 16th District last week announced his challenge to Republican Sen. Ted Cruz, launching an uphill battle in an election cycle critical for congressional Democrats.

O’Rourke, 44, co-sponsored pro-choice legislation such as the EACH Woman Act, which would repeal the Hyde Amendment’s ban on using most federal funding for abortion care. He also co-sponsored multiple iterations of the Women’s Health Protection Act, which would help stop laws targeting abortion providers by prohibiting laws singling them out that don’t apply to other medical services.

“There’s an opportunity to do better for Texas and better for this country. To move past the anxiety and fear, the walls and the refugee bans, and strongly and confidently work together on bringing this state and this country together on jobs, on improving our immigration laws, and on ensuring that we have a Senator working full time for Texas,” O’Rourke said in a Facebook post after making his announcement in El Paso.

Cruz is far from wildly popular among his constituents. A February University of Texas/Texas Politics Project poll found that 29 percent of respondents “disapproved strongly” of Cruz’s performance in Congress, while 20 percent strongly approved.

O’Rourke has acknowledged the race for 2018 won’t be easy. Though President Donald Trump won Texas in the presidential election by the smallest statewide margin since 1996, the state is nonetheless solidly red. And O’Rourke has vowed not to accept campaign donations from political actions committees, potentially putting himself at a fundraising disadvantage.

“I’m under no illusions this will be anything but hard in a primary and anything but hard in a general election. Nothing I’ve ever done that’s amounted to anything has been easy,” he told the Dallas Morning News. “My heart’s in it, I want to do this, I’m driven to do it. I’m not poll-testing it. I’m not consulting with consultants.”

Republicans hold the U.S. Senate with a 52-46 majority, though the chamber’s two Independents caucus with the Democrats. Republicans need eight more seats to win a filibuster-proof majority that would enable the party to push their agenda regardless of Democratic opposition. That means the midterm elections in 2018 will be of the utmost importance in determining whether President Trump can ram through his policy proposals in the coming years.

The Progressive Change Campaign Committee sent a fundraising email to supporters announcing their endorsement shortly after O’Rourke’s announcement. “If he wins, he’ll do more than defeat Cruz—he’ll replace Cruz with a true progressive and land a huge blow on the entire Trump presidency,” the committee said.

U.S. Rep. Joaquin Castro, who represents the state’s 20th District, has expressed interest in entering the race. Matthew Jones, Castro’s political director, said in a statement published by the Texas Tribune that it is “no secret that Joaquin is heavily weighing a Senate run, and he will continue to have those discussions with his family, friends and supporters across Texas.”

“He plans to make his decision in the coming weeks,” Jones said, adding that Castro “has always led the charge on tough fights, so one way or another, he will be on the front lines of the 2018 midterm elections doing everything he can to continue to hold Republicans accountable.”

No matter which Democrat wins the nomination to challenge Cruz, they will face one of Congress’ more ardent anti-choice voices.

Cruz frequently touted his opposition to reproductive freedoms during his bid for the 2016 Republican presidential nomination, vowing to “do everything” within his power to end legal abortion if elected. He embraced noted extremists on the campaign trail like Operation Rescue’s Troy Newman and the Family Research Council’s Tony Perkins, whose organization is considered an anti-LGBTQ hate group by the Southern Poverty Law Center.