Donald Trump is going to war with Scott Walker after being called 'DumbDumb' by one of his supporters

Real-estate magnate Donald Trump has a new target in the Republican presidential primary: Wisconsin Gov. Scott Walker (R).

In recent days, Trump has been going out of his way to bash Walker, apparently out of revenge for being called a "DumbDumb" by one of his fundraisers.

"I'm being very nice to him. And today I read this horrible statement from his fundraiser about Trump. I say, 'Oh, finally I can attack. Finally. Finally.' I would have never done this," Trump said in the middle of a Saturday speech in Iowa.

Trump was referring to a Wall Street Journal report in which Gregory Slayton, a New York venture capitalist and Walker fundraiser, dismissed his candidacy.

"As you've seen Gov Walker is now well ahead of everyone not named DumbDumb (aka Trump) in the national polls," Slayton reportedly wrote in a fundraising invitation.

In his Saturday speech, Trump responded by saying a Walker presidency would be no different from former Florida Gov. Jeb Bush (R) or former Secretary of State Hillary Clinton, the Democratic front-runner. He also tore into Walker's record as governor.

"Wisconsin's doing terribly. First of all, it's in turmoil. The roads are a disaster because they don't have any money to rebuild them. They're borrowing money like crazy," he said. "I wrote this stuff all down, but I don't need it because I have a really good memory - but they projected a $1 billion surplus and it turns out to be a deficit of $2.2 billion. And money all over the place. The schools are a disaster, and they're fighting like crazy because there's no money for the schools. The hospitals and education is a disaster."

He added: "And he was totally in favor of Common Core! Did you know that? He was totally in favor of [Common Core], which I hate."

Trump has feuded with several of his Republicans rivals who have criticized him over his heated rhetoric against illegal immigration and his questioning of Sen. John McCain's (R-Arizona) war record. Trump insulted the intelligence of former Texas Gov. Rick Perry (R), for example, and revealed Sen. Lindsey Graham's (R-South Carolina) personal cell-phone number to his supporters at a rally.

Walker has mostly avoided taking shots at Trump. But his fundraiser's insult apparently opened the floodgates, and Trump is now hitting Walker from all sides.

"I love Wisconsin, it's a great place. But he's putting debt up to gills," Trump said of Walker on CNN's "State of the Union" on Sunday. "The school system is a disaster because they don't have any money. I mean, Walker's state, Wisconsin, is a catastrophe from an economic and a financial standpoint."

Trump, deploying a standard Trump tactic, also highlighted a time when he and Walker were on much friendlier terms. He tossed in some backhanded compliments while doing so.

"I've been nice to Scott Walker. He's a nice guy. He came up to my office like three, four months ago, presented me with a plaque because I helped him with his election. I liked that he was fighting. I didn't know what the hell he was doing, but he was fighting and I like a fighter. Does that make sense?" Trump asked his supporters on Saturday.

He then wondered out loud if Wisconsin taxpayers were on the hook for the plaque he said Walker gave him.

"So I've been very nice to him. But he brings me a beautiful plaque. I don't know who pays for it. Does he pay for that or does Wisconsin pay for it? I don't know," he said. "But it's beautiful."