President Trump (Jabin Botsford/The Washington Post)

Editors’ note: Yesterday, President Trump vetoed a congressional measure to end U.S. involvement in the Saudi-led war in Yemen. We are reposting Sarah Binder’s December analysis of a previous congressional measure to end U.S. involvement in Yemen that noted that even if the measure failed, it was a strong rebuke of Trump’s foreign policy. That analysis remains relevant to yesterday’s veto.

On Thursday, for the first time ever, the Senate used its authority under the 1973 War Powers Resolution to order a president to end U.S. military operations abroad — in Saudi Arabia’s war in Yemen. Then, in a nonbinding resolution, the Senate voted to hold Saudi Crown Prince Mohammed bin Salman personally responsible for the killing of Washington Post contributing columnist Jamal Khashoggi.

The Republican-majority House won’t go along. Even if it did, Trump would be unlikely to sign the measure into law: Each president has challenged the constitutionality of the War Powers Resolution, which Congress enacted over President Richard Nixon’s veto.

But Thursday’s Senate votes were still significant — both for Congress and for the president. Here’s why:

1. These Senate signals are politically important, even if legally ambiguous.

Most notable, of course, is that it is the first time either chamber has used the War Powers Resolution to order an end to the use of military force. Thursday’s vote on that measure included all 49 Democrats joined by seven Republicans.

To be sure, the Constitution directs Congress and the executive to share war powers. Congress has the authority to declare wars, and only Congress can fund them; the president is commander in chief. But both branches contest the parchment divide. Presidents object to congressional encroachments on their commander in chief powers. Legislators complain — though rarely act — when presidents conduct wars without congressional consent.

But Congress more commonly tries to avoid blame for unpopular wars than to challenge the executive’s right to wage them.

The War Powers Resolution asserted congressional power in several ways, including a way for Congress to command the president to bring troops home. An unrelated 1983 Supreme Court decision raised constitutional doubts about one of the key provisions of the law, but Congress revamped the procedure to put it on firmer constitutional ground.

Given all that, the two Senate votes launched an unprecedented strike against the president. The measure had languished in a Senate committee for nearly a year, an orphan backed mainly by Democrats. Then came a perfect storm: abhorrent Saudi behavior; the president’s unwillingness to hold Mohammed responsible for Khashoggi’s murder; and rising public attention to the humanitarian crisis in Yemen. Finally, senators were angry enough to challenge presidential authority.

[When did Congress authorize fighting in Niger? That’s an excellent question.]

The GOP-led House has preemptively blocked any Yemen-related votes this month. But the Senate action will still have consequences.

First, the votes will diminish Trump’s already weakened credibility on foreign affairs. Second, people tend not to pay much attention to foreign policy. But the public will notice this breakdown in elite consensus — further undermining a beleaguered White House. Third, these sorts of congressional signals can influence foreign policy by raising the political costs the president must pay if he wishes to stay the course.

And those are costs a deeply unpopular president can ill afford to pay.

2. The rules of the game matter.

It’s rare that the Senate debates a matter opposed by the majority leader and his party. Indeed, Senate Majority Leader Mitch McConnell (R-Ky.) opposed the war powers measure, even as he supported the resolution to blame the crown prince for Khashoggi’s brutal killing. McConnell argued that for technical reasons the War Powers Resolution did not apply and that it was the wrong war over which to provoke a constitutional crisis with the president.

So how did supporters of the measure get it to the floor?

As political scientist Molly Reynolds explains, the Senate occasionally designs “expedited procedures” that allow senators to take action on select matters, some of which might otherwise not make it to a vote on the Senate floor. War powers resolutions fall into that category. The law allows a majority of the Senate to discharge a measure from committee and bring it to a floor vote — without the threat of a filibuster or leaders’ consent. Many other laws empower majorities in this way.

When the Senate began adopting these procedures decades ago, power was far less centralized in leaders’ hands than it is today. Senators came up with these expedited procedures to challenge executive power and enable simple majorities to act, unencumbered by filibusters. Today, these procedures also help simple majorities and ambitious senators get around the current majority leader’s chokehold on the chamber’s agenda.

3. GOP fractures revealed.

Only seven Republican senators voted against Trump on the Yemen resolution, and one (Jeff Flake of Arizona) is retiring. The remaining six return next year.

On the one hand, that’s hardly a chink in Trump’s wall of GOP support. But in our era of heightened partisanship and polarization, any dissent within the president’s own party about critical war powers is unusual, even startling.

Next year’s new Democratic House majority will likely take up its own Yemen resolution. By then, more GOP senators may join the chamber’s small band — especially if Trump’s mounting legal and political challenges make it more costly for Republican lawmakers to support the president.

[What can House Democrats accomplish with their new oversight and investigative powers?]

The Senate rebuke of the administration’s alliance with Saudi Arabia and its broader Middle East strategy may not be making headlines or crawling across cable news’s breaking news feeds. But even if the specific measure dies with the end of Trump’s Republican Congress, this uprising still stings.