Campaigning Saturday for former Hewlett-Packard CEO Carly Fiorina in San Diego, Sen. John McCainJohn McCainFive key moments from Trump's first 100 days Bottom Line Beyond Manafort: Both parties deal with pro-Russian Ukrainians MORE (R-Ariz.) ripped into fellow Sen. Barbara BoxerBarbara BoxerAnother day, another dollar for retirement advice rip-offs Carly Fiorina 'certainly looking at' Virginia Senate run Top Obama adviser signs with Hollywood talent agency: report MORE (D-Calif.), calling her the "most bitterly partisan, most anti-defense senator in the United States Senate today."

McCain told the crowd at a rally for Fiorina that he has had "the unpleasant experience" of serving with Boxer in the Senate, according to The Los Angeles Times

"When you hear her say that she supports the men and women in the military, my friends, she does not," McCain said, according to the Times. "Because she has never supported the mission, she has never supported victory whether it be in Iraq, or Afghanistan, or anywhere else in the world. Barbara Boxer wants to wave the white flag of surrender and endanger this nation’s national security. It’s time she went back to San Francisco with Nancy Pelosi.”

Boxer faces a tough challenge from Fiorina, who served as co-chair of McCain's 2008 presidential campaign. The latest Field poll in the race shows Fiorina within a point of the incumbent. 

Former Alaska Gov. Sarah Palin, who endorsed Fiorina in California's Republican Senate primary earlier this year, is also in the state Saturday, raising money for the Republican National Committee.

But both Fiorina and California's Republican gubernatorial nominee, Meg Whitman, appear to be keeping their distance.