Democrats in Congress say it would be “illegal” and “catastrophic” if President Donald Trump were to conduct a preemptive nuclear strike on North Korea, and they’re calling on Republicans to be far more vocal on this issue. 

In recent weeks, Trump and North Korean leader Kim Jong Un have been engaged in an ongoing war of words, as the reclusive Asian nation has refused to dismantle its nuclear program and ramped up its long-range missile tests. During his first address in front of the United Nations in September, Trump threatened to “totally destroy” North Korea and has repeatedly suggested he favors a military option over diplomacy in terms of dealing with Pyongyang. The heightened tensions have raised alarms across the world, and many Democrats feel substantive action to prevent Trump from conducting a preemptive nuclear strike is imminently needed. 

“The president would put the existence of the U.S. at risk with a nuclear strike in North Korea,” Congressman Ted Lieu, a Democrat from California, tells Newsweek.

Lieu warns that a preemptive or first-use nuclear strike would not necessarily eliminate all of North Korea’s military assets, which makes such a move so risky. 

“[A preemptive nuclear strike] would be catastrophic. We don’t know where all of North Korea’s weapons are.… If we don’t get their weapons out the first time, we’re screwed. Then they can retaliate with nuclear weapons,” Lieu says. 

In January, Lieu and Democratic Senator Edward Markey of Massachusetts put forward a bill that would prohibit Trump from conducting a first-use nuclear strike without “a congressional declaration of war expressly authorizing such strike.”

Earlier this week, House Minority Leader Nancy Pelosi expressed her support for such legislation.

“There are all kinds of proposals out there, one saying—declaring—the United States of America will not engage in first use of a nuclear weapon. I like that one best,” Pelosi said. 

Democratic Senator Chris Murphy of Connecticut, who sent out an alarming thread of tweets on Trump and North Korea on Monday, tells Newsweek he’s not necessarily opposed to legislation like the bill Lieu and Markey proposed but also feels they are simply restating current law. “A nuclear first strike absent an imminent threat to the U.S. is already illegal,” Murphy says.

Murphy says the best path forward is for Republicans in Congress to step up to let Trump know he doesn’t have the authority to conduct a preemptive strike. 

“I think the first step is for Republican leadership to reiterate the illegality of a first strike against North Korea without congressional approval,” Murphy says. “I don’t know if Trump pays a lot of attention to warnings from me and other Democrats.”

“It’s time for Congress to make very clear that he does not have the power to engage in a preemptive strike without [congressional] authorization,” Murphy adds.

Some have suggested people with military experience advising Trump, including Defense Secretary James Mattis and White House Chief of Staff John Kelly, would somehow move to prevent the president from conducting a preemptive strike if it came to it. 

But Murphy worries Republicans are “overreliant on military leaders inside the White House.”

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Vanity Fair’s Gabriel Sherman told MSNBC’s Chris Hayes on Tuesday “a very prominent Republican” he spoke with had imagined Kelly and Mattis have discussed tackling or physically restraining Trump if he went for the nuclear football. There’s no evidence they’ve had such a conversation. Regardless, Murphy says, “That’s a pretty depressing fallback option to rely on.” 

A small handful of Republicans, perhaps most notably Senator Bob Corker, have expressed concern over Trump’s stance toward North Korea. But Murphy is arguably correct in stating the Republican leadership has remained decidedly silent as the president has banged the war drum, even as polls show a majority of American voters oppose a preemptive strike on North Korea.