Wisconsin Gov. Scott Walker sank to a new low in his effort to fight with real estate mogul billionaire Donald Trump during an interview with Politico’s chief White House correspondent, Mike Allen, at a Koch Brothers-sponsored event in California this weekend. In the interview, Walker accused Trump of acting like a Democrat.

“The governor also weighed in on a pair of Donald Trump’s recent comments, first criticizing the real estate mogul for arguing that Sen. John McCain isn’t an American hero and then also saying Walker has ‘a lot of problems’ in Wisconsin,” Politico’s Daniel Strauss wrote on Saturday, after noting that Walker said he’s ready to run against either Hillary Clinton or Joe Biden, should he be fortunate enough to win the GOP nomination next year.

”On McCain, Walker said ‘no matter what you think of John McCain’s politics, John McCain is an American hero,’” Strauss continued.

“And then, on fire directed at him from Trump, Walker said that the real estate mogul went after him ‘because of something not me or my staff said but a volunteer said, which I think was unfortunate,’” Strauss wrote, quoting Walker.

“More than a week ago Walker fundraiser Gregory Slayton referred to Trump as a ‘DumbDumb’ in a fundraising invitation. All together, Walker said, Trump was basically taking the same attack route as Democrats,” Strauss continued, before quoting Walker in full.

“But he basically used the talking points that the Democrats used over the last four years,” Walker said. “As many of you know, three times we won because those points aren’t accurate.”

Many establishment Republicans have attacked Trump for having been a Democrat in his past, but the line of criticism is largely ineffective because some of the best conservative Republicans—like Ronald Reagan, the former President, or Clarence Thomas, the Supreme Court Justice—are former Democrats.

Walker has slipped in recent polls along with former Florida Gov. Jeb Bush and Sen. Marco Rubio (R-FL), as Trump has risen—something that has shaken the entire Republican establishment.

Walker’s latest attack on Trump came at a Freedom Partners event—an organization funded by the Koch Brothers—in Dana Point, California.

It’s the latest in a brewing bout between the two since a fundraiser for Walker called Trump a “DumbDumb” in an official fundraising invitation sent out by the Walker campaign. Walker and his campaign have not denounced the fundraiser’s comments—which were again, endorsed by his presidential campaign—so Trump went on the offensive in Iowa last week.

After Trump went on the offensive against Walker—as has happened with so many other candidates like Bush and Rubio, among others—Walker dropped in the polls in the key state he needs to win. A new Iowa poll out this week from Gravis Marketing has Walker slipping behind Trump, down 15 points behind the real estate magnate in the Hawkeye State.

“He has got a lot of problems in Wisconsin. You know, Wisconsin has got tremendous problems,” Trump said in a recent interview with Bloomberg Politics, for instance, before adding:

“The debt and the difficult problems that they have going on in Wisconsin that a lot of people don’t understand and know about. Tremendous borrowings. And they have difficulties.”

That Gravis poll of 227 registered Republicans conducted on July 29, with a margin of error of 6.5 percent, shows Trump with 30.9 percent in Iowa. Walker comes in a distant second with just 15.4 percent, a difference well outside the margin of error. Bush gets 10 percent while Louisiana Gov. Bobby Jindal, who’s been tearing it up on the trail in Iowa, surged up to 7.2 percent.

The poll comes after Trump took a commanding lead over Bush, Rubio and Walker in Florida—Bush’s and Rubio’s home state. Walker grew up in Iowa, and has consistently led the GOP field there until now—as Trump surges past him, and Walker keeps sinking as he’s hitting Trump.

Walker, Trump, Bush and Rubio—among others—will meet for the first GOP debate in Cleveland, Ohio, this coming week.