Former congressman J.C. Watts (R-Okla.) comes to the defense of U.S. Senate candidate T.W. Shannon (R) in a new ad, decrying "false attacks" he says opponents have lobbed.

"Now negative ads try to distort his record," Watts says in the commercial. "The truth: T.W. Shannon will oppose more debt and fight to balance the budget."

The backup from Watts comes days after retiring Sen. Tom Coburn (R-Okla.) waded into the race to replace him. In a statement on Thursday, Coburn defended Shannon's main Republican opponent, Rep. James Lankford, against television ads from pro-Shannon groups.

It also comes with a week left until the June 24 primary. Tea party forces like the Senate Conservatives Fund and Sen. Ted Cruz (R-Tex.) have lined up behind Shannon, a former state House speaker, while establishment Republicans are backing Lankford.

There are other candidates in the mix, too. If no one gets a majority of the vote, an Aug. 26 runoff for the top two finishers will be triggered.

According to their pre-primary fundraising reports, Lankford had more than twice as much campaign cash as Shannon for the stretch run.