Colorado Republican State Sen. Owen Hill ended his Senate campaign Monday night and threw his support behind Republican Rep. Cory Gardner, leaving the party largely united behind Gardner to challenge incumbent Democratic Sen. Mark Udall.

“Today I am ending my campaign for the US Senate,” Hill wrote in an email to supporters Monday night. “Thank you for your relentless help and encouragement during this journey. Congressman Cory Gardner has the best chance of defeating Mark Udall in November and I pray that he does.”

Gardner made a late entry into the Senate race, announcing at the end of February after previously declaring that he would not run. With a weak field of Republican contenders considered unlikely to beat Udall, Gardner’s decision to jump in seemed to put the seat in play. Two of the previously announced Republicans moved to clear the way for him — state Rep. Amy Stephens dropped out of the race, and Weld County District Attorney Ken Buck switched races, opting to run for Gardner’s House seat instead.

But not Hill. The state senator refused to drop out, though he said Gardner had asked him to, and lambasted the move as “corruption” and the “party leadership trying to decide who gets to run.”

“This is the exact same corruption and back-room deals that have caused the Republican party to lose elections year after year,” Hill told The Gazette of Colorado Springs after it was reported that Gardner would seek the Senate seat.

Hill had the backing of Tea Party Express, who doubled down on their endorsement of him after Gardner’s announcement. Tea Party Express Chairman Amy Kremer called Gardner the “establishment’s anointed candidate,” and Hill the “clear choice” for conservatives and tea partiers.

Tea Party Express executive director Taylor Budowich said the group had not yet decided their next move in Colorado.*

“We endorsed Owen Hill because we saw him as a promising, young conservative candidate that would match up well against Senator Mark Udall. So while our support remains strong with Owen, a campaign for Senate is a serious decision and Owen must do what’s right for him and his family. We have the utmost respect for Owen and see a bright future for him,” Budowich told The Daily Caller.

“With that said, Senator Udall is vulnerable and we feel we have a great chance at defeating him in November,” he added. “We have yet to make a decision on our next step in Colorado, but we look forward to meeting with Rep. Cory Gardner in the near future to discuss his campaign.”

With Hill out of the race, Gardner has a virtually clear shot at the nomination.

The race between Gardner and Udall is shaping up to be an expensive one: The Koch Brothers-backed Americans for Prosperity made its first ad buy in the race, dropping just under $1 million on a television and online advertising campaign attacking Udall for his support for Obamacare.

A Rasmussen poll released last week showed Gardner to have a good shot at ousting Udall — the two are in a dead heat.

*This post has been updated with Budowich’s comments.

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