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Donald Trump takes aim at Scott Walker: "Finally, I can attack"

No Republican presidential candidate is safe from Donald Trump.

The billionaire businessman set his sights on another contender for the White House Saturday in Iowa, aiming to knock Wisconsin Gov. Scott Walker down a peg after reports surfaced of a Walker fundraiser calling Trump a "DumbDumb."

"I've been nice to Scott Walker. You know, he's a nice guy," Trump told a crowd of supporters Saturday in Oskaloosa, Iowa. "And then today I read this horrible statement from his fundraiser about Trump. I said, 'Oh, finally I can attack. Finally. Finally.'"

The Republican presidential candidate criticized Walker's handling of the Wisconsin budget, saying the state is "doing terribly" and "in turmoil."

"The roads are a disaster because they don't have any money to rebuild them. They're borrowing money like crazy," Trump said. "They projected a one billion dollar surplus and it turns out to be a deficit of 2.2 billion dollars. And money all over the place."

Trump's figures -- which are accurate -- also led him to charge that when it comes to the interest accrued on those debts, Wisconsin "borrowed so much money that a big portion of their budget now is paying for it." What Walker was doing with the financial pitfalls in Wisconsin, Trump said, was "kicking it down the road."

The real estate mogul also attacked that the state of Wisconsin schools, calling them a "disaster" and saying that "they're fighting like crazy because there's no money for the schools." He additionally accused Walker of flip-flopping on his disapproval of Common Core education standards "when he saw he was getting creamed."

Trump targets GOP rivals in feisty South Carolina speech

Walker is just the latest Republican to face Trump's wrath. In recent weeks he has issued blustering attacks against South Carolina Sen. Lindsey Graham ("He's a stiff"), former Texas Gov. Rick Perry ("He put on glasses so people will think he's smart, and it just doesn't work"), even Arizona Sen. John McCain ("He's not a war hero").

In Iowa, Trump stuck with his usual criticisms on the U.S. handling of illegal immigration and the rise of sanctuary cities -- a concept which, he said, "if it wasn't for me, you'd still never have heard of sanctuary cities."

Of the Iran nuclear deal, he slammed the lifting of economic sanctions on the country and warned that the move would make Iran a financial superpower.

"If they were a stock, I would buy so much of Iran right now," Trump said.

In a separate press conference in Oskaloosa, Trump responded to questions about his campaign's recent ban of the Des Moines Register from his events. After Iowa's largest newspaper published a heavily critical editorial urging Trump to drop his presidential bid, the Trump campaign refused to issue press credentials to Register reporters, who operate independently of the editorial board.

The White House contender called the Register "a very liberal newspaper" and added that "when they start writing accurately, they're welcome."

Though he's threatened a third-party run, Trump confirmed that he will continue to run as a Republican candidate.

"I want to run as a Republican," Trump said. "The best chance we have of winning is if I run as a Republican."