But one of Trump's major arguments against the deal is actually incorrect, according to its key architects.
He criticized the agreement for not returning Americans held prisoner in Iran and for the length of time before inspections, but he also raised what he called a little-known point of the deal.
"There's something in the Iran deal that people I don't think really understand or know about," Trump said. "And nobody is able to explain it that if somebody attacks Iran, we have to come to their defense. And I'm saying, does that includes Israel? And most people say, yes. They don't have exclusion for Israel. So, if Israel attacks Iran according to that deal, I believe, the way it reads unless they have a codicil or they have something to it, that we have to fight with Iran against Israel."
Trump was apparently referencing Section 10 of Annex III of the deal, which covers civil nuclear cooperation. That says that Western nations party to the deal will work with Iran on areas including: "cooperation through training and workshops to strengthen Iran's ability to protect against, and respond to nuclear security threats, including sabotage, as well as to enable effective and sustainable nuclear security and physical protection systems."
But his reading of the meaning of the provision was off, according to the State Department.
Secretary of State John Kerry's senior adviser for strategic communications Marie Harf said the language was routine for nuclear agreements.
"This provision of the JCPOA is designed to help bring Iran's nuclear security and safety practices in line with those used by other nuclear programs around the world," Harf told CNN. "The IAEA provides this kind of training routinely, as it is in the interest of all countries that nuclear material be safeguarded from theft and terrorist attacks -- the types of 'sabotage' in question. This would be the focus of any such assistance by the P5+1 or other states. Nevertheless, this provision does not commit any country to engage in this kind of routine nuclear security cooperation, and it is absurd to suggest it [commits] anyone to 'defend' Iran's nuclear facilities."
The Trump campaign did not respond to CNN request for comment on the critique.
Kerry himself also testified before Congress that nothing about the provision compels the U.S. to side with Iran against any attack.
Florida Sen. Marco Rubio, also a Republican candidate for president, asked about this very point in a Senate Foreign Relations Committee hearing in July.
"If Israel conducts an air strike against the physical facility, does this deal, the way I read it, does it require us to help Iran protect and respond to that threat?" Rubio asked.
Energy Secretary Ernest Moniz, a nuclear physicist who helped negotiate the deal, said it categorically does not.
"The purpose of that is to be able to have longer-term guarantees as we enter a world in which cyber-warfare is increasingly a concern for everybody, that if you are going to have nuclear capacities, you clearly want to be able to make sure that those are adequately protected," Kerry added. "But I can assure you, we will coordinate in every possible way with Israel with respect to Israel's concern."
"So, if Israel conducts a cyberattack against the Iranian nuclear program are we obligated to help them defend themselves against the Israeli cyberattacks?" Rubio asked?
"No, I assure you that we will be coordinating very, very closely with Israel as we do on every aspect of Israel's security," Kerry said. "I don't see any way possible that we will be in conflict with Israel with respect to what we might want to do there. And I think we just have to wait until we get to that point."