Democrats proposed a new bill Monday — on the eve of talks between President Donald Trump and North Korean dictator Kim Jong-un — that would prevent the president from launching a pre-emptive strike on North Korea.

Sens. Chris Murphy (D-CT) and Tammy Duckworth (D-IL) introduced the bill, which would require congressional approval before any pre-emptive strike, as an amendment to the National Defense Authorization Act (NDAA).

The legislation is similar to a bill that several Democrats co-sponsored in the Senate last year, and one proposed by Rep. Ted Lieu in the House, which would prevent the president from launching a pre-emptive strike “absent an imminent threat to the United States without express congressional authorization.”

The bill leaves open the problem of how an “imminent threat” is to be determined. It does not answer the question of what North Korea must be expected to do as Congress debates and votes on whether to authorize a pre-emptive military strike by U.S. forces against it.

Though Murphy and Duckworth declared Monday that their preference was for diplomacy over war, arguably their bill achieves the opposite by reducing pressure on North Korea to reach a deal.

It is also unlikely that the bill would pass constitutional muster. While the Constitution provides that only the House of Representatives may declare war, the bill arguably encroaches on the president’s constitutional responsibilities as commander-in-chief of the military.

The purpose of the new bill, and those Democrats have introduced before, has largely been political — that is, to suggest that President Trump is unstable or otherwise incapable of being trusted to act as commander-in-chief.

Joel B. Pollak is Senior Editor-at-Large at Breitbart News. He was named to Forward’s 50 “most influential” Jews in 2017. He is the co-author of How Trump Won: The Inside Story of a Revolution, which is available from Regnery. Follow him on Twitter at @joelpollak.