It has been a feature of the past two-plus years: Republican senators flirt with taking a stand against President Trump on something they disagree about . . . and then back down. Timidity has permeated the official GOP, and the few Trump antagonists pay the price for their apostasies.

But on Thursday, GOP senators might have issued their strongest rebuke of Trump.

The Senate joined the Democratic-controlled House in passing a resolution of disapproval for the national emergency declaration Trump issued to build a wall along the U.S.-Mexico border. In the end, 12 Republican senators — about 23 percent of the 53 in the chamber — voted with all the Democrats to say Trump had gone too far. The GOP senators mostly worried about the precedent it would set if Trump’s successors could declare a national emergency for any reason.

Practically speaking, this probably won’t stop the wall from being funded. Neither chamber passed the resolution with close to the two-thirds majorities they would need to override a veto. Trump will almost definitely just take his loss, issue a veto and move forward.

But practically speaking, the rebuke matters. It matters because it will force what will be his first veto, thereby serving notice that Trump is officially overriding a majority of both chambers of Congress. It also could hurt him in the real venue that will decide whether his wall gets funded: the courts.

It also matters because, regardless of how few dollars or miles of wall this ultimately will affect, it was a real, concrete action taken by an unusual number of Republicans.

When Republicans have rebuked Trump, it has often been in symbolic ways: Jamal Khashoggi, Trump’s trade wars, the withdrawals from Syria and Afghanistan, the media not being “the enemy of the people,” etc.

When it has been on substantive and actionable bills, the defections haven’t numbered as high, or rebukes have been averted altogether at the last moment. When Republicans joined Democrats in balking at the administration’s separation of families at the border, they opted not to vote to end the practice when Trump backed off. When momentum built for a bill to protect special counsel Robert S. Mueller III, it was eventually tabled. They voted in a defense bill to reinstate penalties for Chinese telecom giant ZTE, but then it was excluded in the final bill Trump signed.

Perhaps the biggest substantive rebukes to Trump have been on Russia and Yemen. But Russia wasn’t completely about Trump. Yes, Congress overwhelmingly passed a package of sanctions on the Russians that Trump expressed reservations about. But he signed it anyway. And it wasn’t outside the scope of other actions his administration has taken.

Yemen came just this week. It was quite substantive, but the defections weren’t as big. Seven GOP senators crossed over to vote with Democrats on ending support for the Saudi-led war there, another response to Khashoggi’s death. (Trump may veto that bill, as well.)

Thursday’s vote on the national emergency declaration shouldn’t be overstated. It’s still just a small minority of all GOP senators, and only 13 House Republicans joined them. It’s also an incremental step that may have no ultimate effect on the construction of a wall along the Southern border.

But it’s a step that Republicans have avoided for two years. And it’s one that could contain blowback for all of them. Trump set about trying to make an example of them early Thursday, saying they would all be voting in favor of “crime.”

“A vote for today’s resolution by Republican Senators is a vote for Nancy Pelosi, Crime, and the Open Border Democrats!” he said.

And we’ve seen in recent days how tough this vote could be for some GOP senators. Sen. Thom Tillis (N.C.) wrote a Washington Post op-ed against the declaration and talked about how he was taking a principled stand by voting against it. Then as he faced pushback at home — he’s up for reelection in 2020 — he tried to forge a compromise. Then when that compromise never emerged, he flip-flopped and voted to support Trump on Thursday.

Trump’s whole leadership style involves wielding force and fear via his stranglehold on the GOP base. If Republicans suddenly become more comfortable bucking him, they’ll be emboldened to do it again. This is an important testing ground for that.