Protesters on Friday blocked new Education Secretary Betsy DeVos at a Washington, DC, schoolhouse door — a new low in left-wing “activism.”

Some waved Black Lives Matter placards, but the protest was organized by the Washington Teachers-Union and its parent union, American Federation of Teachers.

Indeed, “black lives matter” is rather DeVos’ own point. She’s spent decades fighting for greater educational opportunity for the poor and underprivileged: Much as the teachers unions want to deny it, that’s the entire point of school choice.

And she’s pointedly started her tenure by embracing minority education. DeVos eventually made it into Jefferson Academy, a predominately African-American middle school, by another entrance, and met with students and staff. The day before, she visited Howard University, a historically black college, to meet with school leaders.

The video of a mob physically denying DeVos access to the school should shock the conscience of Democratic Party leaders and of AFT chief Randi Weingarten.

One person was arrested; DC Metro police are reportedly determining whether DeVos was physically assaulted.

Washington Mayor Muriel Bowser felt obliged to weigh in via Twitter: “We do not condone violence toward anyone,” and “We welcome Betsy DeVos & anyone who wants to learn more about our schools.”

Weingarten herself tweeted: “We don’t condone such acts. We want her to go to [public schools].”

But the fact is, her union set up the protest of DeVos’ visit to a public school — and then failed to control the protesters it recruited for the stunt.

Weingarten and her allies have had their say against DeVos — pushing every Democratic senator, plus two Republicans, to vote against her confirmation. They viciously smeared her as an ignorant, out-of-touch billionaire bigot.

They lost — can’t they at least wait until she does something arguably objectionable before harassing her?

We understand the unions feel threatened by school choice — but that’s no license for teachers to sponsor goonish intimidation.

For shame.