WASHINGTON — Democrats who’ll be chairing top congressional committees next year say they won’t back down on investigating President Trump because he has threatened to release “devastating” documents if they do.

“The President has to learn that he is not above the law and his threats will not intimidate us from doing the work that Congress needs to do,” said Rep. Jerrold Nadler (D-NY), the presumed next leader of the House Judiciary Committee.

Trump told The Post on Wednesday that he’d declassify sensitive documents that would embarrass the Democrats if they engage in “presidential harassment” when they take control of the House in January.

“What he means: If Democrats do legitimate oversight I will burn sources and allies by selectively declassifying info so my legal team can misrepresent it to the public,” tweeted Rep. Adam Schiff, the presumptive new leader of the House Intelligence Committee.

“Why he’s doing it: Fear.”

Trump has been sitting on a trove of classified Department of Justice documents related to the start of the Russia probe that the president’s allies believe will show favoritism toward Hillary Clinton and bias against Trump.

The documents include Justice officials’ request to surveil Trump campaign adviser Carter Page and memos on DOJ official Bruce Ohr’s interactions with Christopher Steele, author of a controversial dossier that alleged Trump ties to Russia.

Trump also wants to release text messages sent by former FBI officials James Comey, Andrew McCabe, Peter Strzok, Lisa Page and Ohr.

Trump told The Post he’ll declassify the documents to counter-punch Democrats.

“If they go down the presidential harassment track, if they want go and harass the president and the administration, I think that would be the best thing that would happen to me,” Trump said. “I’m a counter-puncher and I will hit them so hard, they’d never been hit like that.”