Gov. Arnold Schwarzenegger will endorse John McCain on Thursday, giving a certain boost to the Republican presidential front-runner six days before California's high-prize primary. The two will appear at a news conference after touring a Los Angeles-based solar energy company and the governor will make his endorsement official, his senior aides confirmed Wednesday. Schwarzenegger's endorsement is yet another setback for Mitt Romney, the former Massachusetts governor who saw Florida slip from his grasp Tuesday after McCain rolled up the support of that state's two top elected Republicans, Gov. Charlie Crist and Sen. Mel Martinez.