Republican presidential candidate Donald Trump boasted Sunday that he's responsible for Democratic rival Bernie Sanders' recent polling surge over front-runner Hillary Clinton.

Trump, who is leading in most Republican presidential polls, said during a campaign stop in Muscatine, Iowa, that the Vermont senator rose after he attacked Clinton's husband, former President Bill Clinton, for his infidelities. 

“When I hit Hillary and Bill last week—but I did the right thing—but they start saying, 'Bernie Sanders is surging, an amazing thing is happening.' I did that. I did it,” Trump told his audience, adding, “This guy Bernie Sanders, give me a break. They say he's a socialist, some would say he's a communist.”

Trump said it'd be “too easy” to attack Sanders right now, and he added that he didn't want to attack Sanders too much because it might benefit Republicans if Clinton and Sanders continue to attack each other for a bit longer.

He shrugged, then added: “I have stuff in my mind. He would drop so fast.”

Sanders, an independent who caucuses with Senate Democrats, has made significant gains on Clinton in Iowa polls ahead of the Feb. 1 caucuses. A CBS poll released earlier Sunday found that Sanders is leading Clinton in Iowa by a 47 to 46 percent margin.

Sanders also holds a double-digit lead against the former secretary of state in New Hampshire ahead of the Granite State's Feb. 9 primary, but Clinton maintains a formidable national lead.

Trump didn't just go after Democrats on Sunday. He also continued to attack his Republican rival Senator Ted Cruz of Texas, who is polling slightly below him in Iowa.

“Everybody hates him,” Trump told the crowd. “He's in the U.S. Senate and not one senator has come out to endorse him.”

Trump continued to poke fun at Cruz's Canadian birth and he once again criticized Cruz for not disclosing loans from Goldman Sachs and CitiBank during his 2012 Senate campaign.

“He'll run for president,” Trump added, “then he'll run for prime minister of Canada.”

The capacity crowd of more than 1,000 people inside a high school gymnasium laughed in approval.

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