The principal at a progressive Manhattan private school told parents in an email last week that the Trump presidency was more troubling than Vietnam, the assassination of Martin Luther King Jr., the September 11 attacks and Watergate, The Post has learned.

Steve Nelson’s scorching missive managed to roil several parents at the $46,000 per year Calhoun School – no small feat considering the Upper West Side bastion’s blaring liberal bent.

“It was inappropriate, it was offensive, it was condescending,” said one parent. “This is a liberal school. So I guess that’s the approach. But this was too much. To compare this to 9-11 – I think that’s just too much.”

Nelson emailed a series of anguished ruminations on Donald Trump’s ascent to Calhoun parents, simultaneously calling for non-partisanship while skewering the billionaire’s policies.

In a message sent last week, Nelson, who also teaches journalism at the pre-K through 12 campus, noted his intimate familiarity with several recent catastrophes – including 9-11.

“I watched soot-covered New Yorkers grimly trudging north on West End Avenue on September 11, 2001,” Nelson wrote. “I am more troubled now.”

Elsewhere in the lengthy missive, Nelson acknowledged the theoretical need to avoid political bias in a school environment. “One in my position must be scrupulous in avoiding partisanship,” he said.

But he later asserted in the same message that “there are matters that transcend political diversity.”

“The ways in which equity and equality are now threatened are deeply troubling, including the constitutionally suspect and arguably discriminatory efforts to restrict or prohibit immigration based on religion and/or ethnicity,” he wrote.

READ MORE FROM THE NEW YORK POST.