It’s no surprise that Harris’ campaign was very happy with it.

“The Vice President is proud to have earned Congresswoman Cheney’s vote,” campaign manager 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 every American who wants to reject the chaos and division of Donald Trump, turn the page, and forge a new path 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 to work to earn your support.”

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

I realize that the former congresswoman is persona non grata in today’s GOP circles, but in case anyone has forgotten, Cheney was and is deeply conservative. We’re talking about a lifelong Republican from a prominent Republican family, who was an unabashedly far-right lawmaker who served as chair of the House Republican Conference — a leadership position she won while running unopposed.

During Trump’s presidency, she voted with the Republican White House about 94 percent of the time, a higher score than some members of the House Freedom Caucus.

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, and that’s why she’s supporting his opponent.

There is of course room for debate about the impact this could have and whether a meaningful number of voters will be swayed by the former legislator’s announcement. But I would not be too quick to dismiss the significance of the approval.

Voters have heard repeatedly in recent weeks and months from Republican critics of Trump who have publicly stated (a) that they cannot bring themselves to support their party’s nominee; and (b) that they cannot bring themselves to vote for the Democratic ticket either. These GOP voices often say they plan to write in the name of another prominent figure they respect.

This week, for example, former Sen. Pat Toomey joined that contingent, telling CNBC, “If you lose an election and you try to overturn the results so you can stay in power, you lose me. You lose me on that point.” However, the Pennsylvania Republican added in the same interview that he also disagrees with Harris.

But that’s what makes Cheney’s announcement so remarkable: She didn’t just announce 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 major party’s two nominees will be sworn in in January.

This isn’t particularly 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.