Donald Trump has warned Democrats against launching a series of investigations into his presidency - vowing that he is a "counter-puncher" who will unleash fury.

Speaking to The New York Post, Mr Trump warned of consequences if the Democrats - who take control of the House in January - use their new-found power to investigate him.

“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," he said.

"I’m a counter-puncher and I will hit them so hard they’d never been hit like that."

He said he could declassify FISA warrant applications and other documents from Robert Mueller’s probe — and predicted the disclosure would expose the FBI, the justice department and the Clinton campaign as working in coordination to set him up.