John McCain's campaign has seized on comments his primary rival made about whether the Republican senator would have made a better commander in chief than President Obama.
Hayworth told a Tea Party gathering in Phoenix this week that having a Democrat in the White House was better than a moderate Republican.
"I think the last thing we needed was a progressive trying to wear a Republican cloth coat as president of the United States," he said.
Hayworth said later that he voted for McCain in 2008 but won't "make that mistake" in the Aug. 24 primary.
The McCain camp released a Web video Friday that's critical of Obama's record since taking office, but notes Hayworth would still prefer the Democrat to McCain.