Three weeks after the Sept. 11, 2001, terrorist attacks, Congress passed the Authorization for Use of Military Force (AUMF), a law that gave the president the authority to use “all necessary and appropriate force” against “nations, organizations, or persons,” involved in the 9/11 attacks. The AUMF helped launch the ongoing conflicts in Afghanistan and Iraq. On Wednesday, 18 years after it was passed, House Democrats passed an appropriations bill that includes a provision that would repeal the AUMF, HuffPost reports.

Reporters Matt Fuller and Amanda Terkel note that three presidents have invoked the AUMF for more than three dozen military engagements in 14 countries. While some House members, notably Rep. Barbara Lee, D-Calif., oppose the bill, it took a Democratic majority in the House and the possibility of the Trump administration using it as a justification for war with Iran for the repeal vote to succeed.

The administration has launched attempts to demonstrate links between Iran and al-Qaida. As Charlie Savage writes in The New York Times, “In public remarks and classified briefings, Trump administration officials keep emphasizing purported ties between Iran and [al-Qaida].” They’ve done so “despite evidence showing their ties aren’t strong at all. In fact, even [al-Qaida’s] own documents detail the weak connection between the two,” Vox’s Alex Ward reports.

On Tuesday, Secretary of State Mike Pompeo told reporters that President Trump “does not want war” with Iran. On Wednesday, after Iran shot down a U.S. surveillance drone overnight, Trump tweeted that “Iran made a very big mistake,” before backtracking and suggesting to reporters that perhaps someone “loose and stupid” in Iran had screwed up, maybe accidentally. But while the president may be waffling in his rhetoric on Iran, his close advisers, including Pompeo and national security adviser John Bolton, have been much clearer.

Since Trump appointed Iran hawk Bolton and shortly afterward pulled out of the Iran nuclear deal, observers have questioned whether his administration is preparing for another war in the Middle East. In January, The Wall Street Journal reported that the National Security Council, at Bolton’s direction, asked the Pentagon to provide military options for striking Iran.

A younger generation of House members may have been a factor in the AUMF repeal provision. Some of the newer members are up to three generations younger than the entrenched leadership, many of whom are in their 70s. That means, as Fuller and Terkel point out, that “some of the newest members of Congress grew up with the Iraq War in the background of their high school and college years. Many of them opposed the invasion and saw politicians ― many of whom are now colleagues ― send their friends off to war.”

But members of Congress who spoke to HuffPost reporters pushed back against the generation-divide explanation. Rep. John Yarmuth, a 71-year-old Kentucky Democrat, said, “Very few are on a different page.” Rep. Gil Cisneros, D-Calif., who is 48, echoed Yarmuth, saying, “I don’t think there’s any divide on that situation at all.” And Lee, who cast the lone dissenting vote when the AUMF passed in 2001, is 72.

The repeal of the AUMF consists of just 11 lines in a larger House appropriations bill, and would go into effect eight months after it passes—if it passes, that is. As Fuller and Terkel note, the law faces an uphill battle in the Senate:

This is the first serve in an appropriations pingpong match between the Democratic House and the Republican Senate. Senate Majority Leader Mitch McConnell (R-Ky.) ― much less Trump ― is unlikely to accept such a repeal.

Democrats also may face obstacles within their own ranks. They weren’t able to repeal the AUMF when they had control of all three branches of government from 2009 to 2011. There’s also the question Fuller and Terkel raise: whether Democrats in either the House or Senate are willing to shut down the government over the issue. “If Democrats aren’t willing to risk a shutdown over repealing this 2001 military authorization,” they write, “then they’re almost already giving up the game.”