Sen. Bernie Sanders (I-VT) has a fallback plan to save his push to get the U.S. out of the disastrous Yemen war—a plan that’s become ironically necessary since the House of Representatives, which voted for withdrawal just two weeks ago, accidentally compromised its chances in the Senate.

On the surface, it’s a parliamentary effort to rescue something that has become a signature foreign policy achievement for the socialist senator as he runs for president. But beneath, the episode underscores just how difficult it is to get the U.S. out of a war—no matter how brutal the conflict, nor how peripheral it is to American security interests.

This latest development could prompt the Senate to vote on getting the U.S. out of the Yemen war as early as next week. But the Sanders camp’s Plan B puts the effort back to something like square one.

“Fortunately, we’re prepared to move quickly on the Senate version of this resolution, so the Republicans’ cynical shenanigans in the House have only delayed, not prevented, the effort to end U.S. support for the world’s most destructive war,” a Sanders aide told The Daily Beast.

On Feb. 13, the House passed a resolution by Sanders ally Rep. Ro Khanna (D-CA) that called U.S. military aid to the Saudi-led coalition in Yemen a violation of the 1973 War Powers Resolution, which reasserted Congress’ constitutional authority for warmaking in the wake of Vietnam. Backed by House Democratic leadership and fueled by anger at Saudi Arabia for the grisly murder of journalist Jamal Khashoggi, it passed 248-177, though it wasn’t quite the victory progressives had sought.

But House Republicans tacked onto the Yemen resolution an amendment expressing support for Israel and declaiming antisemitism, an unsubtle attack aimed at Rep. Ilhan Omar (D-MN) for a tweet her enemies seized upon to call the Muslim congresswoman anti-Semitic. The amendment passed overwhelmingly, but the process jeopardized the antiwar maneuver’s passage in the Senate.

That’s because the House language introduced something technically termed “non-germane” to the Sanders-Khanna resolution. That in turn screwed up a legislative maneuver known as “privilege” intended to route around Mitch McConnell (R-KY), who opposes the anti-war effort, and bring the resolution to the Senate floor without going through the foreign-relations committee. On Monday, the Senate parliamentarian ruled that the House-passed resolution had lost privilege because of the Israel/anti-Semitism amendment.

To save the Yemen extrication, Sanders, who last week announced a second run for president, is turning to a Plan B. Instead of pushing ahead with the House version, Sanders will instead move to discharge the exact same resolution that the Senate passed in December, a resolution that both matches the initial House language and has already been ruled as privileged, so it can come to the floor. Sanders and his allies, Republican Mike Lee of Utah and Democrat Chris Murphy of Connecticut, will call on their colleagues to pass the same measure in the current Congress.

Then, they’ll ask Khanna to get the House to re-pass the measure it passed earlier this month. It’s going to be a tough ask, but there’s brewing outrage amongst sympathetic House Democrats over the opportunity the parliamentarian’s ruling hands McConnell. Eliot Engel, a relatively conservative New York Democrat who chairs the House foreign-affairs committee, called it “just disgraceful” and a signal that the Senate GOP is out to bury the Yemen withdrawal.

For his part, Khanna is on board, his office told The Daily Beast.

“Rep. Khanna will support Sen. Sanders’ plan to move this forward in the Senate. Once the senate passes the resolution, it will come back to the House for a vote and the Congressman will work with leadership and the [Congressional Progressive Caucus] to see it head to the president,” said Heather Purcell, Khanna’s spokesperson. “And meanwhile, Rep. Khanna is hopeful the president may still sign it, though we know it’s an uphill battle. It would be hypocritical to be for withdrawal in Afghanistan and withdrawal in Syria and then say we need to be involved in the Saudi war in Yemen.”

Erica Fein, the advocacy director for Win Without War, said the fallback plan still had a “better than 50-50 shot” of passage.

“We have been in the Forever War in 80 countries around the world since 9/11,” Fein said. “U.S. support for the war in Yemen is indicative of the way in which Congress has ceded its author to the executive branch, and it’s only after years and years of working to educate and build support that we’re able to have a chance at ending support for the Yemen conflict.”