But Pelosi has a much more immediate way to challenge Trump’s declaration. Under the National Emergencies Act, or NEA, both chambers of Congress can pass a resolution terminating any presidentially declared national emergency.

[Let’s say Trump declares a national emergency. What happens next?]

What Pelosi can do

Elizabeth Goitein, who has researched this topic extensively for the Brennan Center for Justice, tells me that if Pelosi exercises this option, it will ultimately require the Senate to vote on it in some form as well. The NEA stipulates that if one chamber (Pelosi’s House) passes such a resolution, which it easily could do, the other (McConnell’s Senate) must act on it within a very short time period — forcing GOP senators to choose whether to support it.

Alternatively, Goitein notes, the Senate could vote not to consider that resolution or change its rules to avoid such a vote. But in those scenarios, the Senate would, in effect, be voting to greenlight Trump’s emergency declaration.

The NEA lays out a timetable for this process, and by Goitein’s reading, it would all take place within the protracted period of barely longer than a month. “In short, there could be 36 days between introduction of the resolution in the House and a vote on the Senate floor,” Goitein told me, “but that vote would have to happen,” and once it did, one way or the other, it would put senators “on record.”

A Democratic leadership aide tells me the House might opt for this move if Trump takes the plunge. “The House will vigorously challenge any declaration that seeks an end run around Congress’s power of the purse,” the aide says.