Texas Rep. Beto O’Rourke on Friday became the first Democratic challenger to Sen. Ted Cruz in what will be an uphill fight between the possibility of a primary to toppling a conservative hero in a deep red state.

In announcing his candidacy in his hometown of El Paso, O’Rourke said the incumbent was putting his own interests ahead of his constituents, saying he would be “a senator who is not using this position of responsibility and power to serve his own interest, to run for president, to shut down the government,” and said the state needed “a senator who is working full-time for Texas.”

Cruz’s team sent out a fundraising email pointing to an Associated Press report showing that some of O’Rourke’s colleagues are already calling him “Senator.”

“Despite any record of achievement and a progressive ideology out of touch with the majority of Texans, Beto O’Rourke will have the full support of the mainstream media and a Washington establishment willing to do everything in their power to see Ted Cruz defeated,” the email read.

While O’Rourke is the first Democrat in the race, he potentially won’t be the only one — Rep. Joaquin Castro, like O’Rourke is a three-term incumbent, is weighing his own challenge to Cruz.

O’Rourke has a history of toppling giants. In 2012, he won an intensely personal primary against incumbent Rep. Silvestre Reyes, despite the fact Reyes was endorsed by then-President Barack Obama.

Liberal group Progressive Change Campaign Committee cited that race in its endorsement of O’Rourke sent after his Friday announcement.

“Beto defeated a corrupt, corporate Democratic incumbent in a primary in 2012,” the group said in a fundraising email. “That’s why some call Beto a giant slayer.”

But O’Rourke’s progressive credentials might make dragon-slaying tougher against one of the most conservative senators. O’Rourke is one of the few members of Congress who supports legalization of marijuana.

He also supports of comprehensive immigration reform and a pathway to citizenship for undocumented immigrants. He recently teamed up with some Republicans to co-sponsor a bill that would allow parents of U.S. citizens banned from re-entry for minor violations to have their statuses adjusted.

He’s not an orthodox liberal on trade, though, having voted to give the Obama administration Trade Promotion Authority, which would subject trade deals to a simple up-or-down vote without the ability to amend.

O’Rourke could face a tough primary against Castro, should he decide to run, said Colin Strother, who has worked on campaigns with both Castro and his two brother Julian, who was mayor of San Antonio before serving as secretary of Housing and Urban Development in the Obama administration.

Strother said he doesn’t know what Joaquin Castro will decide but that he has a history of taking on big challenges. Castro made his first run for state legislature against a six-year incumbent and won.

“I don’t think either of them are afraid of a challenge,” Strother said of the Castro brothers.

And O’Rourke will face a well-funded campaign in Cruz, who quickly became a national conservative leader as the face of the tea party in the Senate and from his presidential race last year.

Democrats are defending 23 seats in the Senate next year, which will make them selective in which races they can put money into.

Campaigning in Texas is expensive and O’Rourke would media markets in San Antonio, Dallas, Austin, and Houston, as well as widespread rural areas.

“National Democrats can invest in two or three states for what it costs in Texas,” said Matt Angle, director of the liberal group the Lone Star Project.

Inside Elections with Nathan Gonzales rates 10 of the seats they’re defending as anything but a lock.

Cruz has earned enemies since being elected to the Senate in 2013 — not just among Democrats but also many of his Republican colleagues — Angle joked that Cruz has “all the charisma of a toothache.”

Still, Mark McKinnon, a Texas-based political consultant who worked on former President George W. Bush’s presidential campaigns, said Cruz is doing better with allies. Rumblings of potential primary challenges has mostly simmered down.

“The challenge for O’Rourke or Castro is that Cruz has effectively rehabilitated himself with Republican primary voters, eliminating a primary challenge,” he said.

On its surface, Texas is still a state where Trump beat Hillary Clinton by 9 points. Democrats have also held no statewide seats since 1994 and the last Democratic senator Texas elected was Sen. Lloyd Bensten in 1988.

But Clinton did better what Obama did in the state in 2012, when he lost the state by 15.8 points. 

According to an analysis from the liberal website the Daily Kos, three Republican-held congressional districts broke for Clinton: those of Reps. Pete Sessions, John Culberson and Will Hurd.

“We didn’t field a Democrat against Sessions,” Strother pointed out.

O’Rourke also gained some national attention when he and Hurd livestreamed their two-day drive from Texas to Washington, D.C., where they took questions from viewers and debated topics like health care and immigration from viewers.

Strother said O’Rourke could capitalize on the frustration some in the state are feeling with Trump. One example he cited was a Democratic woman’s group in Gregg County, where Trump won 69 percent of the vote, whose membership has grown to 450.

“I think there’s a desire to be at the tip of the sword of this thing,” Strother said.

Correction April 1 12:30 p.m.| A previous version of the story contained an incorrect figure about Trump’s victory margin in Texas