Rep. Seth Moulton Seth MoultonThe Hill's Morning Report - Presented by Facebook - Markey defeats Kennedy; Trump lauds America's enforcers in Wisconsin Moulton fends off primary challenges in Massachusetts Portland: The Pentagon should step up or pipe down MORE (Mass.), a 2020 Democratic presidential candidate, on Sunday criticized President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE, saying a weak U.S. commander in chief makes the world more dangerous and increases the chances of the nation getting dragged into war with Iran.

The Marine veteran told ABC "This Week" host George Stephanopoulos George Robert StephanopoulosColbert implores Pelosi to update 'weaponry' in SCOTUS fight: 'Trump has a literal heat ray' Murkowski: Supreme Court nominee should not be taken up before election Cruz says Senate Republicans likely have votes to confirm Trump Supreme Court nominee MORE that he's concerned about a Gulf of Tonkin-like incident taking the U.S. to war with Iran, just as the original incident helped start the Vietnam War.

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He said national security advisor John Bolton John BoltonMaximum pressure is keeping US troops in Iraq and Syria Woodward book trails Bolton, Mary Trump in first-week sales Ex-NSC official alleges 'unprecedented' intervention by White House aides in Bolton book review MORE is pushing for war, adding that President Trump, having not served in the Vietnam War, "lacks the credibility to keep us out of this one."

"The fact of the matter is there are a lot of dangers we're facing around the world because we have a weak commander in- chief in Donald Trump. That's why in this race I'm taking him on not just as president but as commander in chief," Moulton said.

"We've got to start talking about how to make America safe and strong, from our communities to our border to across the globe to restoring America's leadership," he added. "And you do that through strength, you do that by showing how America will make the world stronger and safer together."

Moulton touted his Marine credentials and first-hand perspective of fighting in the Middle East to make his case, saying he had fought Iranians in Iraq.

"It was bloody. We won. And if necessary I will fight Iran again," he said. "But right now war is not necessary."