A GOP congresman on Sunday backed former Rep. J.D. Hayworth (R-Ariz.) who announced Saturday he will primary Sen. John McCain (R-Ariz.)

Rep. Dana Rohrabacher (R-Calif.) became the first lawmaker to endorse the former radio host Hayworth's upstart bid.

In a Twitter post, Rohrabacher said:

McCain's wrong on too many big issues: #Immigration, #GlobalWarming, #Bailouts. @JDHayworth is better #AZ #tcot #Hayworth

Hayworth informed the Associated Press late Friday that he was stepping down as host of an Arizona talk radio program to run for Senate against the 2008 GOP presidential nominee. 

By law, Hayworth could not remain a radio host and run for Senate.

The former congressman is challenging McCain from the right. McCain is perceived by some in the Republican Party as someone who too often bucks his party, though he has recently scored points among the GOP faithful for opposing the Democrats' healthcare reform bill plan. 

Hayworth was unseated in 2006 by Democrat Harry Mitchell.

Cross-posted to theTwitter Room