Updated 11:55 a.m. |The Club for Growth’s political action committee formally endorsed Republican Rep. Tom Cotton on Wednesday, a day after the freshman announced a challenge to Democratic Sen. Mark Pryor in Arkansas.

The group is set to launch a six-figure TV ad buy against Pryor on Thursday, tying the incumbent to President Barack Obama. The ads will run on broadcast and cable stations, and it’s just the latest media campaign targeting one of the most vulnerable incumbents of the cycle.

“Tom Cotton is a taxpayer hero and a fighter against the Obama agenda,” Club for Growth President Chris Chocola said in a statement.

In a top pickup opportunity for Republicans, Cotton is the rare recruit who has coalesced support from both Republican party leaders and conservative outside groups. This is the group’s second endorsement of the 2014 cycle and its first public backing of a Senate candidate.

The endorsement is not surprising, as the group was strongly supportive of Cotton’s 2012 House bid. And along with the super PAC arm of the Senate Conservatives Fund, the Club for Growth had already targeted Pryor on TV. The two groups jointly released a poll in March that offered encouraging results for Cotton.

The SCF stopped short of endorsing Cotton in a statement on Wednesday, but SCF Executive Director Matt Hoskins indicated it was open to doing so “if he leads on the big issues and excites the grass-roots in Arkansas.”

Pryor released a video statement on Tuesday ahead of Cotton’s formal announcement. It was critical of the freshman congressman’s voting record in his first seven months on Capitol Hill.

“I don’t know who Mr. Cotton’s been voting for, but it hasn’t been for Arkansas,” Pryor said. “When you vote against student loans and against the farm bill and you vote to cut Medicare and Social Security, you’re not voting for Arkansas, you’re carrying someone else’s water.”

The second-term senator also released his second TV ad this week. It was similarly critical of Cotton’s record so far in Congress. A campaign spokesman declined to offer details of the size of the ad buy.

In an interview Tuesday with The Associated Press before his announcement speech in his hometown of Dardanelle, Cotton made it clear what the campaign will be about.

“Mark Pryor, by his voting record over the last four and a half years, has proven that he now stands with Barack Obama, not with Arkansas,” Cotton said.

The race is rated a Pure Tossup by Rothenberg Political Report/Roll Call.

Update: The Pryor campaign spent $42,600 to run its one-minute ad on broadcast stations on Tuesday and Wednesday, according to a GOP source tracking ad buys. Watch the ad here:

https://www.youtube.com/watch?v=OTZpvmkVRYQ