Our role in the seven-year conflict in Yemen has been robust enough that many experts believe the Saudi-led coalition would sue for peace without it. It has been robust enough that American lawmakers — including a bipartisan majority of senators in 2019 and Representatives Pramila Jayapal, Democrat of Washington, and Peter DeFazio, Democrat of Oregon, this year — have characterized it as a violation of Article I of the Constitution, which grants Congress the power to declare war, and of the 1973 War Powers Resolution, which sharply limits, in nature and timeline, military action initiated by the president.

We crossed the line in Yemen, those lawmakers concluded, even if it’s not wholly clear where the line is.

And what we’ve done in Yemen looks a lot like what we’re doing in Ukraine. Last month, leaks by U.S. officials revealed that the United States helped Ukraine to kill Russian generals and strike a Russian warship, and Mr. Biden signed a $40 billion aid package for Ukraine, a lot of which is for military assistance like weaponry and intelligence sharing. The bill, which Ms. Jayapal and Mr. DeFazio voted for, comes on top of billions of prior military support. The Biden administration also announced, this month, that it will send rocket systems to Ukraine that could theoretically strike inside Russian territory, and it reportedly has plans to sell the Ukrainian government four drones that can be armed with Hellfire missiles.

Are we at war in Ukraine? If we swapped places — if Russian apparatchiks admitted helping to kill American generals or sink a U.S. Navy vessel — I doubt we’d find much ambiguity there.