Far-right Texas Rep. to challenge conservative Sen. John Cornyn

Sen. John Cornyn, R-Texas, appears on CBS' "Face the Nation"

In a last-minute move Monday evening, conservative Rep. Steve Stockman, R-Texas, filed papers to give up running for re-election in the House order to mount a primary challenge against Sen. John Cornyn, R-Texas.

Cornyn is a two-term incumbent and the second-ranking Republican in the Senate with strong conservative credentials. Stockman, however, said he was compelled to challenge Cornyn, the Senate Minority Whip, because the senator "betrayed" Sen. Ted Cruz, R-Texas, by declining to back his strategy to shut down the government in October over Obamacare.

"You and I are in a foxhole fighting to save this constitutional Republic, but liberal John Cornyn is bayoneting us in the back," Stockman said in a statement on his website. "Liberal John Cornyn wakes up every morning and works to make the Senate a more liberal place. That's why I am running for the United States Senate. I have a 100% pro-gun, pro-life, conservative voting record in Congress."

Cornyn is already running against a few lesser-known candidates in the March 4 primary, the Texas Tribune reports, but with nearly $7 million in cash on hand as of October, he will be hard to beat.

Additionally, Cornyn -- the former chairman of the National Republican Senatorial Committee -- is considered to be a solid conservative. His re-election campaign is already backed by Gov. Rick Perry, R-Texas, and he has a 94 percent rating from Americans for Prosperity, the conservative political advocacy group backed by the billionaire Koch brothers.

While Cruz has declined to endorse Cornyn, the Texas senators are still working together -- last week they filed a joint amicus brief to the Ninth Court of Appeals in Texas in a case concerning the display of religious content at schools.

Chris Chocola, president of the influential conservative group the Club for Growth, said in a statement that the Club for Growth PAC is likely going to stay out of the primary, given both Stockman's and Cornyn's conservative records.

"Our PAC evaluates three factors when looking at races that involve incumbents: 1) the strength of the incumbent's record; 2) the degree of difference between the incumbent and the challenger on economic issues; and 3) the viability of the challenger," he said. "None of those factors weigh against Senator Cornyn, so we do not expect to be involved in the Texas Senate race."

Stockman, meanwhile, came under scrutiny this year for failing to disclose in federal filings all of his business affiliations. He has, however, proven to be very conservative since rejoining the House this year after first serving from 1995 to 1997.

Stockman's taken a hardline conservative position on immigration, and gun control -- in January, he threatened to impeach President Obama over his efforts to use his executive authorities to reduce gun violence. In February, just two months after the mass shooting in Newtown, Conn., Stockman brought musician and gun advocate Ted Nugent as his guest to attend Mr. Obama's State of the Union address.

In an interview with Texas Monthly in September, Cornyn lamented the ongoing fueds between tea party conservatives and the rest of the Republican Party.

"I don't know how we got off on this track where some people are welcome in our party and some people are not," he said. "Hence my reference to Ronald Reagan's line, 'What do you call someone who agrees with you eight times out of ten? An ally, not a twenty-percent traitor.' Well, we're at a point where you can agree with someone 98 percent of the time, but they think of you as a 2-percent traitor, which is just an impossible standard."