"Wisconsin is in turmoil," Trump told a boisterous crowd at a rally in Iowa. He pointed to the state's roads, schools and hospitals, which he said were all "a disaster."
Walker, who is leading polls in Iowa, remains one of Trump's biggest rivals in the race.
"I hear the only person beating me in Iowa is Scott Walker," he said. "I can't believe I'm in second place. Folks, will you please put me in first place so I feel better?"
Trump told the crowd Saturday that he had helped Walker win his race because he admired the candidate's "fight," but didn't know what he was fighting for. "I've been very nice to him," he said.
But after Walker's fundraising email went public, Trump declared: "I can finally attack."
I think Trump is a buffoon, but, if the Vichy GOP put up JEB, I'll cheerfully vote for His Donaldness.