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 (D-Mass.), who has launched a 2020 campaign for president, on Monday responded to a question about a hypothetical alien invasion with a dig at 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's immigration policies.

"I would not build a wall between here and Mars," Moulton said on BuzzFeed News's "AM to DM" the same day he announced his run for the White House. "I would not do that."

New 2020 candidate (and Bill Pullman lookalike?) @sethmoulton on what he would do if he were president during an alien invasion: "You gotta start with diplomacy." pic.twitter.com/H1RFaXB7Ps — AM2DM by BuzzFeed News (@AM2DM) April 22, 2019

"No, you got to start — and this is serious, guys — you got to start with diplomacy," he continued. "You always have to start with diplomacy."

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Moulton backed his diplomacy-first approach by quoting former Defense Secretary James Mattis James Norman MattisBiden courts veterans amid fallout from Trump military controversies Trump says he wanted to take out Syria's Assad but Mattis opposed it Gary Cohn: 'I haven't made up my mind' on vote for president in November MORE, who served as a general when Moulton was in the Marines.

"General Mattis, when he was General Mattis, not Secretary Mattis, was my division commander. And he said ... 'If you cut the State Department budget, you got to buy me more bullets,'" Moulton said, adding that he would offer the alien "a classic American meal."

"I'd serve a beer and a burger, and then if the meeting goes well, that’s all good," Moulton said jokingly. "If the meeting starts to not go so well I'd say, 'By the way, that burger — that’s the last aliens who visited.'"

Moulton, 40, joined a massive field vying for the 2020 Democratic nomination on Monday. He said in a video that he is running because "we have to beat Donald Trump, and I want us to beat Donald Trump because I love this country."

Moulton is one of a few veterans in the Democratic field. South Bend, Ind., Mayor Pete Buttigieg and Rep. Tulsi Gabbard (D-Hawaii) are also running for the nomination.

The three-term congressman's comments about a hypothetical alien invasion come as Trump moves forward with his plans to build a wall along the U.S.-Mexico border. Trump declared a national emergency earlier this year to fund it after failing to secure funding from congressional spending bills.

The Pentagon in March transferred $1 billion from its accounts to help build Trump's long-sought wall.