Washington (CNN)Donald Trump says the United States got hosed in the deal it and other world powers struck to halt Iran's nuclear program because "the Persians are always great negotiators."
Donald Trump: 'Our country's going to hell'
"They are laughing at us back in Iran," he said in an interview with CNN's Dana Bash.
He said the agreement is reminiscent of one the United States struck to secure the release of Army Sgt. Bowe Bergdahl, trading five Taliban officials.
"They get their five guys that they most wanted, anywhere in the world. Who makes deals like that?" Trump said.
He blasted President Barack Obama's administration for failing to secure the release of four U.S. citizens who are imprisoned in Iran on espionage charges.
"Why couldn't they make that part of the deal? It would have happened quickly -- easily if you had the right messenger," Trump said. "And that should have actually happened earlier. That should have happened at the beginning of the negotiation."
He also said the United States shouldn't let up on its economic sanctions against Tehran. If he was in the Oval Office, Trump said, he would have "doubled and tripled up the sanctions, and I would have made a much bigger deal."
In the interview, Trump also took shots at Hillary Clinton, the Democratic presidential frontrunner who he said has "problems" -- in the name of Sen. Bernie Sanders, who he compared to Obama in the 2008 primary.
He said he's decided to ramp up his attacks on Clinton after her blistering comments in an interview with CNN about his controversial remarks about undocumented immigrants from Mexico.
"We're too worried about tone in this country and that's why we're getting beaten by everybody. It's about results. You have to get results," Trump said.
Asked by Bash about a Monmouth University poll released Monday that showed nearly 40% of Republican voters think he's running just for publicity, Trump also said more Republicans will decide to vote for him once they realize he's dead serious about becoming the next president.
"Why would I be doing this? I take abuse from everybody, and I'm doing this for fun? This isn't fun -- I want to make America great again," Trump said.
The real estate mogul was asked about polls that show many Republicans still don't take his candidacy seriously.
"I think it's a great thing for me," Trump said. "Because a lot of those people want to vote for me, but they think that I'm doing it for publicity. The fact is, that was one (poll result) I was very surprised at."
He said he's taking the process seriously, and will release personal financial disclosures "over the next couple of days" that "will show an unbelievable company."
"I built that. I built it," he said. "And that's what this country needs. We need that. I mean, our country's in so much trouble. China, Japan, Mexico, everyplace. Name a country, every deal we have with every country is a bad deal for us. And that's what's wrong. I mean, we need jobs, we need manufacturing back."
He wouldn't comment on Republicans who have criticized the direction Trump's ascension up GOP primary polls has steered the party's nominating process.
"I don't know about that. I'll be honest with you. I want to save the country," he said. "Our country's going to hell. We have a problem. I want to make America great again. And to do that, you have to be bold, you have to be strong, you have to use the same abilities that I use. We don't have that in office right now. We have people that are incompetent."