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President Trump told supporters in Indiana Thursday evening that the U.S. would not agree to a redux of the 2015 Iran nuclear deal when he sits down with North Korean dictator Kim Jong Un in Singapore next month.

"I think it's going to be a very big success," Trump told a rally in Elkhart, "and if it isn't, it isn't. We're not going to be walked into an Iran deal where the negotiator, [then-Secretary of State] John Kerry, refused to leave the table."

Trump, who was joined in Indiana by home-state Vice President Mike Pence, spoke two days after he announced that the U.S. was withdrawing from the Iran nuclear accord, which was negotiated by the U.S. and five other world powers along with the Tehran regime.

"The Iran deal was one of the most embarrassing agreements the United States has ever entered into," said Trump, who added that the U.S. "cannot allow [Iran] to have nuclear weapons."

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"We have to be able to go into their military bases to see whether or not they’re cheating," he said before adding sarcastically, "Now, of course we’re all sure they’re not cheating, but just in case."

The president also said that the relationship between the U.S. and North Korea is "good" and praised Kim for agreeing to the release of three American detainees, whom Trump greeted at Andrews Air Force Base early Thursday, as a prelude to the summit.

"I think that Kim Jong Un did a great service to himself, to his country, by doing this," said Trump, who added "we're going to set the table, we're going to make a great deal for the world, for North Korea, for South Korea, for Japan, for China. So what he did was the right thing."

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Trump traveled to Indiana two days after Republican voters nominated former state lawmaker Mike Braun to challenge vulnerable Democratic Sen. Joe Donnelly, whom the president dubbed "Sleepin' Joe."

Trump said Donnelly would "do whatever Chuck Schumer and Nancy Pelosi tell him to do." Donnelly, Trump said, will "say one thing in Elkhart" and then support the "radical, liberal agenda. It never, ever fails."

"This November, Indiana will face an important choice: You can send a really incredible swamp person back to the Senate like Joe Donnelly," the president said, "or you can send us Republicans like Mike Braun to drain the swamp."

At one point, Braun took the stage to say a few words, casting himself in the mold of Trump.

"I’m a businessman and an outsider, just like our president," Braun said. "And you can count on me to be a true reinforcement and the guy that is going to retire Joe Donnelly."

Trump touted strong economic numbers during his appearance, but also warned his audience that "all of the great momentum that we’re having as a country; on jobs on safety, on security, on our military, it’s all at stake in November."

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He also brought up Pelosi's statement this week that her party would try to undo tax cuts passed by Republicans last year.

"I don’t think her party was too happy," Trump said. "But you know what? That’s her thought, that’s what they want to do. They want to raise your taxes [and] end your tax cuts, they want to have open borders where everyone flies into our country."

"The strides that we’re making have never, ever been made like this before," the president added. "But it can also disappear if you put fools and if you put the wrong people in [office]. ... You have to work every day between now and November to elect more Republicans so that we can continue making America great again."

After the rally, Donnelly said in a statement it was "okay" that Trump and Pence were "here today for politics, but problems only get solved when you roll up your sleeves and put in the hard work."

"I'm Indiana's hired help in the Senate because I don't work for any president or any political party -- I work for Hoosiers, and that will never change," he said. Donnelly's campaign said the senator had voted with Trump 62 percent of the time.

The Associated Press contributed to this report.