As Saudi Arabia’s crown prince arrives in Washington for a diplomatic trip that doubles as confirmation of his geopolitical emergence, his U.S.-backed prosecution of a devastating war in Yemen may prove a stumbling block.

If things break the way three senators seek, then as early as Tuesday, the Senate will debate and then vote on ending U.S. military refueling, targeting analysis and other assistance to the Saudi war on Houthi-controlled Yemen. That war, for the past three years, has featured indiscriminate civilian bombing and facilitated a mass famine and cholera outbreak. And its primary mover is the Saudi defense minister and heir apparent, Mohammed bin Salman, ubiquitously known as MBS, who is slated to meet with President Trump at the White House on Tuesday.

It’s been a long procedural road for a resolution pushed by independent Bernie Sanders, Democrat Chris Murphy, and Republican Mike Lee to end aid for the Yemen war. Their resolution, introduced in the Senate foreign relations committee on March 1 and therefore ripe for a move to the floor, holds U.S. assistance in that war in violation of the 1973 War Powers Resolution. The resolution’s remedy is not to a congressional vote to authorize aid to the Saudis, but to stop it outright.

“I don’t think anyone could’ve predicted this would occur when the Crown Prince was in Washington, but I think the upcoming public debate on the Saudis’ devastating war in Yemen will send a strong signal about Congress’s growing reticence to continue fueling this conflict,” Murphy told The Daily Beast.

“ We believe U.S. military support for the Saudis’ war in Yemen is illegal, immoral and harms national security. ” — Sen. Chris Murphy

As early as Tuesday afternoon, The Daily Beast has learned, the senators will push for a so-called motion to discharge the resolution from the committee. If they get a simple majority, it will proceed to the Senate floor for a lengthy period of debate that may stretch into Wednesday. The debate would culminate in a vote, also by simply majority, on immediately ending U.S. military assistance to the Saudi forces MBS commands.

All this comes with procedural hurdles. The Pentagon rejects the “fundamental premise” of the antiwar resolution. Its acting top lawyer wrote to Senate majority leader Mitch McConnell last month that “the limited military and intelligence support that the United States is providing to the [Saudi]-led coalition does not involve any introduction of U.S. forces for purposes of the War Powers Resolution.” The resolution’s backers expect that McConnell or another senator will raise that issue to preempt a floor debate.

But the antiwar senators think that they have the stronger argument. Section 8(c) of the resolution defines the “introduction of United States Armed Forces” to include servicemembers who “participate in the movement of...military forces of any foreign country or government when such military forces are engaged.” Since U.S. tanker aircraft that refuel Saudi warplanes that bomb Yemen necessarily facilitate military movement, the senators think they can bat back a challenge to their resolution on those grounds.

The 32-year old MBS, the son of ailing octogenarian King Salman, rapidly consolidating power, and a portion of that effort runs through Washington. After MBS cultivated Jared Kushner and Trump himself, resulting in Trump’s rapturous reception in Riyadh in May, MBS felt free in November to purge and imprison actual and potential rivals for the levers of Saudi control, particularly the economic ones. While MBS billed it as an anti-corruption effort, the fantastically wealthy Saudis he detained at the Ritz Carlton surrendered what the New York Times called “huge sums of money… [and gave] government control of precious real estate and shares of their companies,” giving it the air of a shakedown. “Only death,” MBS told 60 Minutes on Sunday, can stop his ascension to the throne.

After a triumphal heir-apparent tour of Egypt and Britain, MBS and a gigantic retinue are en route to the U.S., which is “his gateway to becoming king,” said Ali al-Ahmed, director of the Institute for Gulf Affairs and a critic of the royal family.

A Senate fight on Yemen during his visit will make him “very upset,” al-Ahmed believes, as “the man does not like to be told no… He feels entitled to get his way. When he hears from the Senate that that’s what the U.S. wants, if that’s what they say, he’ll be extremely upset.” As defense minister, MBS “does not run away from [the Yemen war], he owns it, he says it’s necessary,” al-Ahmed said.

The U.S. military doesn’t go that far, but it has made clear it considers support for its anti-Iran friend in Riyadh more important than the starvation, disease and deaths of millions of Yemenis. Even though the Murphy-Sanders-Lee resolution does not restrict the military from attacking suspected terrorists in Yemen, a Pentagon document for senators acquired by HuffPost portrayed counterterrorism as collateral damage from a successful resolution, intimating that “Saudi Arabia may reallocate resources from counterterrorism to the counter-Houthi fight.”

Trump plans on discussing the Yemen war with MBS as well, according to a senior administration official who briefed reporters on Monday. But the administration will emphasize mitigating the humanitarian disaster the war has unleashed more than it will expect the Saudis to end the war.

“We’re going to continue to assist Saudi Arabia with legitimate defense needs, including its rights to defend its borders, but also push them, work with them to determine the political way forward to advance the long-term stability of Yemen, end the suffering of the Yemeni people [and] resolve many of the grievances which extremists, such as al-Qaeda in the Arabian Peninsula, have exploited,” said the official, who characterized U.S. support for the Yemen war as “actually very modest.”

It’s far from certain that the three senators will actually get their floor vote. Staffers concede that there are parliamentary maneuvers that the resolution’s antagonists might launch to obstruct the measure or strip out its demand for an end to U.S. assistance. All involved recognize a lack of precedent for the Senate to force the U.S. out of an unauthorized war.

But after three years of the U.S. facilitating the decimation and immiseration of Yemen, senators opposed to the war have perhaps their best shot at both ending the U.S. role and making it a liability for the Saudi heir.

“We believe U.S. military support for the Saudis’ war in Yemen is illegal, immoral and harms national security,” Murphy said, “so yes, it’s good that we have an opportunity to ensure the war in Yemen is one of the main topics of discussion here in Washington during the Crown Prince’s visit.”