When the “Republicans for Harris” rollout began in earnest a month ago, the effort featured some fairly prominent names, including former GOP governors, members of Congress, and even Republicans who served on Donald Trump’s White House team. In the days and weeks that followed, the list of Republicans backing Vice President Kamala Harris continued to grow.

There was, however, one name in particular that many political observers in both parties were keeping an eye on: What would former Rep. Liz Cheney do?

That question now has an answer. NBC News reported:

Former Rep. Liz Cheney, R-Wyo., on Wednesday endorsed Vice President Kamala Harris for president, the latest high-profile Republican endorsement for Democrats. Cheney’s comments took place during an appearance at Duke University’s Sanford School of Public Policy.

“It is crucially important for people to recognize — not only is what I’ve just said about the danger Trump poses something that should prevent people from voting for him, but I don’t believe we have the luxury of writing in candidates’ names, particularly in swing states,” the Wyoming Republican said.

“As a conservative, as someone who believes in and cares about the Constitution, I have thought deeply about this. And because of the danger that Donald Trump poses, not only am I not voting for Donald Trump, but I will be voting for Kamala Harris.”

Not surprisingly, the Harris campaign was delighted.

“The Vice President is proud to have earned Congresswoman Cheney’s vote,” campaign chair Jen O’Malley Dillon said in a written statement. “She is a patriot who loves this country and puts our democracy and our Constitution first. … Vice President Harris will be a president for all Americans, regardless of political party. For any American who is looking to reject the chaos and division of Donald Trump, turn the page, and pursue a new way forward that protects our freedoms and defends the American values we all believe in, there is a place for you in the Harris-Walz coalition, and we will continue working to earn your support.”

For those who’ve followed Cheney’s career, this announcement was hardly inevitable. In fact, a decade ago, it would’ve been inconceivable.

I’m mindful of the fact that the former congresswoman is persona non grata in contemporary GOP circles, but in case anyone’s forgotten, Cheney was, and is, very conservative. We’re talking about a lifelong Republican from a prominent Republican family, who was an unapologetic far-right lawmaker who served as the House Republican conference chair — a leadership post she won while running unopposed.

During Trump’s presidency, she voted with the GOP White House roughly 94% of the time — a higher score than some members of the House Freedom Caucus.

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But despite this record, Cheney — the Republican co-chair of the bipartisan Jan. 6 committee — recognizes the unique threat her party’s nominee poses to the American political system, so she’s backing his opponent.

There’s room for debate, of course, about the kind of impact this might have and whether a meaningful number of voters will be influenced by the former lawmaker’s announcement. But I wouldn’t be too quick to dismiss the endorsement’s significance.

Voters have heard repeatedly in recent weeks and months from Republican critics of Trump who’ve publicly declared (a) they can’t bring themselves to support their party’s nominee; and (b) they can’t vote for the Democratic ticket, either. These GOP voices tend to say they intend to write in the name of some other prominent figure they respect.

Just this week, for example, former Sen. Pat Toomey joined this contingent, telling CNBC, “When you lose an election and you try to overturn the results so that you can stay in power, you lose me. You lose me at that point.” The Pennsylvania Republican added in the same interview, however, that he disagrees with Harris, too.

But that’s what makes Cheney’s announcement so notable: She didn’t just declare her intention to vote for Harris, she subtly reminded her party’s other anti-Trump voices that they face a binary choice. One of the two major-party nominees will be sworn into office in January.

This isn’t especially complicated: As Cheney made clear, if you recognize Trump as a unique threat to the American experiment, you have a responsibility to support the person — the only person — who stands between him and the White House.

Will this inspire other Republicans to follow Cheney’s lead? Watch this space.