The U.S. still backs Saudi Arabia's fight in Yemen, even though Congress voted to end that support. Now, progressive Rep. Ro Khanna (D-Calif.) is pushing Democratic leaders to turn to the Supreme Court to help enforce Congress' will.

Why it matters: Congress' resolution seeking to end U.S. involvement in Yemen passed with support from diverse ideological factions — from moderates to Bernie Sanders to Rand Paul, only to meet a veto from President Trump.

That has united a similarly diverse group of law professors, who say Trump usurped Congress' authority over matters of war when he vetoed the resolution and that the House should sue him for it.

"I think the Speaker is seriously considering pursuing the lawsuit and will make the correct next step for the people of Yemen and our constitutional integrity," Khanna told Axios. "Yemen can’t wait, and it is my hope that this legal challenge to Trump’s veto moves forward."

"If Nancy Pelosi gets a majority behind her to bring suit, this is a moment of truth for the Supreme Court," said Yale law professor Bruce Ackerman, who's leading the charge on this legal theory.

The response: "We continue to consider all viable options to end this humanitarian crisis," Pelosi's office said.

The big picture: The Constitution gives Congress the power to declare war, and in the wake of Vietnam, Congress spelled out more detailed rules about presidential unilateral power. In Ackerman's view, the Yemen vote is a referendum on whether those rules still apply.

The big question: The Supreme Court has said presidential power is "at its lowest ebb" when exercised in a way that's "incompatible with the ... will of Congress." If the House sues over Trump's Yemen veto, the central question would be whether that's what happened here, said Scott Anderson, a Brookings fellow and former State Department lawyer.

Ackerman says it obviously is. Trump's veto "defied fundamental principles of constitutional law," he and 12 other law professors wrote in a letter to Pelosi.

Between the lines: The case is likely a long shot, given the Supreme Court's ideological balance as well as Chief Justice John Roberts' traditional reluctance to get in the middle of disputes between the other two branches.

The courts would have to toss aside a decades-old interpretation of certain parts of Congress' war powers, Anderson said, adopting a new standard for America's work with other countries' militaries.

"Courts have been really resistant and reluctant to take up these questions," he said.

What's next: If Congress wants to force the U.S. out of Yemen, its best bet might be to keep trying with different legislative vehicles, Anderson said.