This story has been updated.

Democratic Sen. Christopher Murphy has the most frightening possible assessment of the Trump administration’s standoff with North Korea: The prospect of war is very real, and Congress needs to move quickly to prevent President Trump from leading the US into a conflict that could kill hundreds of thousands of people.

Murphy has been warning for weeks that he believes Trump is serious about wanting to go to war with Pyongyang. In an interview earlier this month with Vox’s Ezra Klein, Murphy said Pentagon officials are speaking about North Korea with a very different tone than they’d used in the past, a shift that has led him to conclude that armed conflict with the Kim Jong Un regime was a distinct and growing possibility.

Murphy’s own thinking about how to stave off a conflict with North Korea has also been evolving. When he spoke to Klein on October 10, the senator said it would be extremely difficult to “pass legislation pre-constraining [Trump’s] ability to manage foreign policy in the Korean Peninsula.”

Now, though, that’s basically what Murphy and seven other colleagues want to do. The group of senators — which also includes 2016 presidential candidate Bernie Sanders and Democrats Elizabeth Warren and Cory Booker, both possible Democratic presidential candidates in 2020 — introduced new legislation Tuesday that would prevent Trump from launching an attack on North Korea, or from spending any money on a military strike, unless North Korea had struck first or Congress had given the White House the green light to do so.

My bill w @brianschatz & @CoryBooker makes clear that any unauthorized preemptive strike on N Korea - nuclear or conventional - is illegal. — Chris Murphy (@ChrisMurphyCT) October 26, 2017

The bill’s prospects are deeply uncertain. The chair of the Senate panel that would consider it, Republican Sen. Bob Corker, has warned that Trump is an unstable and dishonest leader who is undercutting efforts to resolve the North Korean crisis through diplomacy rather than war. That would seem to make him a natural supporter of the new bill. A Corker spokesperson, however, declined to comment about whether he would back the new push.

I spoke to Murphy about the threat of war with North Korea, why he believed his bill could help prevent it, and why it might be a mistake to assume that the generals who surround Trump — the so-called “adults in the room” — would keep him from launching a strike rather than prodding him to do so. Our conversation, edited for length and clarity, is below.

Yochi Dreazen

What would this bill do in practice?

Chris Murphy

The administration seems to be suggesting that if North Korea obtains an ICBM [intercontinental ballistic missile] capable of hitting the United States, that would justify military action without congressional support. That's preposterous. This bill would make clear that absent an imminent threat to the United States, you need congressional authorization before you can act.

I simply do not believe that the Constitution gives the president the ability to conduct military action abroad absent an attack on the United States, or an imminent threat of attack. But the president's advisers seem to be suggesting that they perceive his powers to be much broader than that. This legislation would clear up that discrepancy.

Yochi Dreazen

It seems like the bar Trump is setting for when he might use force is even lower than North Korea getting a long-range missile. In some of his comments, Trump has said he’d act if even if all North Korea does is continue to make threats against the US or its allies. In other words, North Korea’s threatening rhetoric in and of itself could be enough to justify a strike.

Chris Murphy

That's exactly right. We hear military leaders talk in terms of a closing window. The idea seems to be that the administration is interested in acting before, not after, the regime gets the ability to reach the United States with a nuclear weapon. There's just no conceivable way that's allowable without congressional authorization, especially if you're talking about a larger-scale military attack.

Yochi Dreazen

The Obama administration used the Authorization for the Use of Military Force that was passed after 9/11 to justify the fights against ISIS in Iraq and Syria. Is your concern that with North Korea, there isn’t an AUMF of any sort?

Chris Murphy

I think the jump from the 2001 AUMF to the fight against ISIS is illogical, but at least the Obama administration tried to make it. If the Trump administration uses broad Article II authority to justify an attack against North Korea, there is literally no end to their ability to make war without Congress. Congress would be wholly and completely irrelevant in the question of overseas military action.

Yochi Dreazen

The War Powers Act was meant to do the same type of thing, wasn't it? To constrain a president by making them go to a coequal branch of government before launching a war?

Chris Murphy

In some ways, what we're talking about is slightly more permissive than the War Powers Act. The War Powers Act has only three circumstances under which the president can undertake military action: a declaration of war, specific statutory authorization, or an attack on the United States. The War Powers Act doesn't actually talk about an imminent attack. Our legislation will also include the threat of imminent attack.

Yochi Dreazen

Are there any Republican co-sponsors?

Chris Murphy

No. I'll admit to having moved this pretty quickly so as to not have time to negotiate it with Republicans, but there's nothing in here that Republicans couldn't support.

Again, it does contemplate military action being potentially permissible in the case of an imminent attack against the US. The problem is that the floor of the United States Senate is largely shut down right now. If this were 20 years ago, this proposal could be on the floor in the next few weeks for a vote, because it used to be that senators had the ability to offer amendments on the floor. I think if Cory and Brian and I were able to get this on the floor, I wouldn't be surprised if it drew enough Republican votes to get it to or close to 60 votes.

Yochi Dreazen

Tell me more about the specific structure of the bill.

Chris Murphy

We're writing this as a funding limitation. It would say that the administration cannot take military action, and can use no funds for military action, unless there is an attack, an imminent attack, or you’ve gotten congressional authorization.

Yochi Dreazen

I know when you talked to Ezra a couple of weeks back, you were saying even then that there was this drumbeat toward war that had you very literally scared that it might happen. Are you feeling like that drumbeat is getting louder? Or is it about where it was a couple of weeks ago?

Chris Murphy

I'm not more worried than I was when I raised alarm bells a few weeks ago, but I’m definitely not less worried. Part of it is that we are strangely relying on military leaders to convince the president not to take military action. History doesn't justify that confidence. Military leaders have trained for a long time to use the tools at their disposal, and when they find a president who is willing to put them into the field, they often take advantage of that. Maybe he didn't have people whispering in his ear that he should decertify the Iran nuclear agreement, but I'm pretty sure somewhere up and down the chain of command, he's got somebody telling him that the military is ready to go.

Yochi Dreazen

I feel like people have basically been projecting their own hopes onto the generals that Trump’s surrounded himself with, and trying to persuade themselves that the generals will keep him from doing anything too crazy. But now we’re seeing John Kelly debase himself and be dishonest, and we're seeing H.R. McMaster become much more political than many of his predecessors. This idea of the adults in the room seems to have just fallen by the wayside.

Chris Murphy

Some of the generals seem to be falling into the same patterns of the president, and that's really hard to watch. At the same time, I listened to [Defense Secretary Jim] Mattis and [Secretary of State Rex] Tillerson give a closed-door briefing to members of the Senate. It was by and large reassuring. This was two months ago, before some of the alarm bells started to go off for me. But I have heard Mattis and Tillerson walk through a pretty conventional, well-thought-out approach to try to bring North Korea to the table.

So, as much as I'm worried about which way the military may eventually push him, I do have some confidence that there are some high-level advisers around the president telling him that a military first strike absent an imminent threat is a bad idea. I don't have a lot of visibility into the White House, but I'm sure there are some people telling him it's a bad idea.

Yochi Dreazen

When you were talking to Ezra, you talked about how difficult it would be to try to “preauthorize or de-authorize military authority” when it came to North Korea. What changed, from thinking that wasn't necessarily a good idea to saying we need to do this?

Chris Murphy

I don't think it's inconsistent. What I was saying is that it's hard to micromanage ahead of time what military interventions, under what circumstances, are permissible and what aren't. I don't think this new bill is micromanagement by any means. I think this is a restatement of his constitutional authority and our constitutional authority. Admittedly the president may disagree, which is why this bill is important.

Yochi Dreazen

But what’s the substantive difference between a bill that would manage what he could do on the battlefield and a bill like this one that would try to prevent him from being able to launch the strike in the first place?

Chris Murphy

It's difficult to put tactical limitations on a president's warmaking power absent any vision of what the theater looks like. I have said that if we pass a war authorization against ISIS, I think it should have tactical limitations. But I can say that because I can see the theater that exists right now in the Middle East. I can't see the theater yet in North Korea. That's what I'm talking about.

Yochi Dreazen

So to put in another way, there’s already fighting happening against ISIS, so the bill could say that Trump couldn’t move the battle beyond the borders of Iraq and Syria?

Chris Murphy

Exactly, or it shouldn't involve ground troops. I have greater confidence in Congress's ability to put tactical limitations on our authorization in the Middle East than I do when it comes to North Korea.