"Now, the Iranians are watching the way he engages with North Korea, and vice versa," Graham said of Trump. "So, we've got a chance here to deliver some fatal blows to really bad actors in 2018. But if we blink, God help us all," he said.
Graham spoke the same day Iran's government limited access to social media during the fourth day of anti-government protests that resulted in the deaths of two people on Saturday.
Trump has been publicly supportive of the protests on Twitter, repeatedly saying the United States and the rest of the world are "watching" how the events unfold.
Graham also dismissed the notion that Trump's support of the protests is counterproductive, referring to such thinking as "the Obama approach."
"If I were Trump, I'd do the exact opposite of Obama," Graham said. "Obama said: 'I don't want to get involved. I don't want to mess up the chance of getting a deal with Iran.' Well, the deal with Iran hasn't worked. The money didn't go to benefit the people, it went to benefit the Ayatollah and his henchmen."
He suggested the president should appear on television using the Iran protests as a reason why the United States should withdraw from the Iran nuclear agreement in 2018.
"If I were President Trump, I would have a nationwide address pretty soon explaining why the Iranian nuclear deal is a bad deal for the world, what a better deal would look like, and urge Congress and the European allies to get a better deal with Iran -- before it's too late," Graham said.
Ret. Navy Adm. Michael Mullen -- a former head of the Joint Chiefs of Staff under both presidents George W. Bush and Barack Obama -- said the U.S. is closer to nuclear war with North Korea than ever and warned that Iran could rapidly develop nuclear weapons if Trump ends the Iranian nuclear deal.
"I worry greatly about the fact that the Iranians will bring forward a nuclear weapon capability," Mullen said while appearing on ABC News This Week on Sunday. "They were very close when the deal was struck. They can redevelop it, I think, very rapidly."
He said Trump has been successful in getting China to take a more active role in trying to restrain North Korea's nuclear activities, but also warned Trump's presidency has been "incredibly disruptive, certainly unpredictable in many many ways."
"A real measure of how this all comes out is whether China is going to commit to a peaceful resolution here. If they don't, then I worry a great deal that it's much more likely there will be conflict," he said.
Mullen added that America's enemies benefit in this "incredibly dangerous climate."
"Those who have been our friends for many years ask questions about our commitments to them... and our enemies, those that would do us ill, seem to be able to take advantage of the uncertainty," he said.