WASHINGTON - Top US Democrat Nancy Pelosi gave the green light Thursday to draft articles of impeachment against Donald Trump, as the embattled president vowed he would "win" the coming fight.

By asking the House Judiciary Committee chairman to draw up the charges, Speaker Pelosi signaled that a formal vote on impeaching the 45th American president is all but assured.

With a majority of the Democratic-controlled chamber already expressing intent to back the divisive procedure, Trump is likely to become just the third president in US history to be impeached by the House of Representatives.

"Sadly, but with confidence and humility, with allegiance to our founders and a heart full of love for America, today I am asking our chairman to proceed with articles of impeachment," Pelosi said in a televised statement.

Trump "has engaged in abuse of power, undermined our national security and jeopardized the integrity of our elections," she said, adding "the president leaves us no choice but to act."

A defiant Trump dared Democrats to press ahead with impeachment "now, fast" -- so he can have a "fair trial in the Senate" where his party holds power and he is confident of being exonerated.

"The good thing is that the Republicans have NEVER been more united," Trump tweeted. "We will win!"(FA)