“I support the nominee of the party. If I change my mind, I’ll let you know,” McCain said in Arizona earlier this month. The remarks were quickly included in a TV ad by his likely Democratic opponent Rep. Ann Kirkpatrick (D-Ariz.).

Democrats argue McCain’s refusal to break ties with Trump—even after he suggested the GOP senator wasn’t a war hero because he was captured in Vietnam—highlights that he’s lost his independent streak after decades in Washington.

“John McCain has endorsed Donald Trump more than 50 times, despite the nominee’s dangerous and divisive attacks,” said D.B. Mitchell, a spokesman for Kirkpatrick’s campaign. “[It’s] another clear example to Arizonans that McCain’s ‘straight talk’ days are gone, and he now cares more about saving his political career than doing what’s right.”

Outside groups, including MoveOn.org and People for the American Way, and national Democrats have also seized on the message, while Minority Leader Harry Reid (D-Nev.) said McCain is “running like a scared dog.”