U.S. Rep. Seth Moulton used harsh words to describe the Oval Office meeting between President Donald Trump, Vice President JD Vance and Ukrainian President Volodymyr Zelenskyy.

“I thought it was a meeting between two total cowards who are puppets of Vladimir Putin,” Moulton told Boston Public Radio on Monday, referring to the American leaders. Moulton said Trump and Vance had sold out an American ally, Ukraine, and were unwilling to stand up to Russian President Putin, who Moulton called a “murderous dictator.”

Trump and Zelenskyy were meeting to discuss a potential deal for the U.S. to access rare earth minerals in Ukraine in exchange for military aid to defend themselves against Russia. The meeting turned heated , with Trump saying Zelenskyy was disrespectful and never said “thank you” for previous aid the U.S. provided.

Moulton, who sits on the House Armed Services Committee, said he considers Trump and Vance’s actions as threats to American national security.

“This is about the fact that Putin will clearly go somewhere next, and it’s probably going to be a NATO country where we have American troops stationed,” he said. If U.S. troops die, Moulton warned that could escalate to nuclear exchange.

The congressman said the Trump-Zelenskyy meeting also sent a message to other United States’ adversaries on how the U.S. might respond to similar situations. For example, China President Xi Jinping wants to take over Taiwan, which is currently a self-governing island. According to Moulton, what’s stopping China is the threat of American deterrence. If Jinping invades Taiwan, it could escalate into a world war, he said.

The Oval Office exchange differs from what Moulton experienced with his Republican colleagues at the Munich Security Conference last month, where a bipartisan group of lawmakers met with Zelenskyy and European allies.

“We were all united, Democrats and Republicans, saying, ‘Yes, we’re going to stand with our allies. Of course we will,’” Moulton said. After the Oval Office exchange, however, Moulton was dismayed by Republicans’ lack of criticism of the president.

“This is about our national security,” Moulton said. “That’s not a partisan issue. It’s about keeping America safe.”