What will it take to keep the United States Holocaust Museum free of political interference and manipulation?

The problem first popped up soon after its founding a quarter-century ago, then faded — until now, it appears.

The museum, in conjunction with the US Institute for Peace, was set to unveil a study on Syrian war crimes on Monday. The report claims it was near-impossible for then-President Barack Obama to “take effective action to prevent atrocities.”

In other words, the study — which relies on “computational modeling and game theory methods” — is basically a whitewash of Obama’s abandoning of his self-proclaimed “red line” against Syrian strongman Bashar al-Assad.

Oh, and the study was overseen by a former Obama intelligence and national-security official.

Happily, Tablet magazine published advance excerpts of the report, and the reactions were so strongly negative that the museum quickly pulled it from its Web site.

It’s not hard to see why: The museum’s mission extends beyond just the Nazi genocide of Jews. But, as literary critic Leon Wieseltier notes, that mission hardly includes rewriting history to “justify or excuse official inaction” in an ongoing genocide.

Making this report even more blatantly partisan is the fact that several Obama administration officials — including Ben Rhodes, an architect of his Syria policy — are members of the museum’s board.

In 1993, shortly after the Holocaust Museum opened, President Bill Clinton’s State Department pressured the museum to invite Croatian leader Franjo Tudjman, despite his anti-Jewish writings.

Five years later, State similarly pushed the museum to invite PLO leader Yasser Arafat — not to educate him, but to burnish his image. When the museum’s director objected (and was overruled by White House pressure), he quit.

The National Academy of Public Administration, at Congress’ request, later issued a report decrying the “inappropriate” politicization of the taxpayer-funded museum and calling for reforms.

That report said the Holocaust Museum in particular “should not be used as a tool to achieve particular political purposes.” Too bad that sage advice has been forgotten.

A museum of conscience, as this one purports to be, should never abandon it — or allow it to be hijacked.