Top US Democrat Nancy Pelosi gave the green light on 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."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!"....This will mean that the beyond important and seldom used act of Impeachment will be used routinely to attack future Presidents. That is not what our Founders had in mind. The good thing is that the Republicans have NEVER been more united. We will win!— Donald J. Trump (@realDonaldTrump) December 5, 2019Pelosi did not announce the charges against Trump, but they could include abuse of power, obstruction of Congress and obstruction of justice.'Absolute control' in Senate"The president abused his power for his own political benefit," Pelosi said, by withholding military aid and a White House meeting in exchange for Kiev's commitment to investigate Joe Biden - his potential Democratic rival in the 2020 election."If we allow a president to be above the law, we do so surely at the peril of our republic," added the speaker.The White House, which has refused to cooperate with the inquiry, said Democrats should be "ashamed" for pulling the impeachment trigger.The process is expected to move rapidly from here on, with articles likely presented for a full House vote later this month after weeks of hearings.Democrats do not want impeachment and a subsequent Senate trial to suck up too much political oxygen just as voting kicks off to determine their party's presidential nominee for 2020.On Wednesday, three constitutional scholars told the Judiciary Committee that the president's actions seeking foreign interference in US elections were clear grounds for removal.NightmareBut a fourth, called by Republicans to testify, told the panel there was "inadequate" evidence for impeachment.Top House Republican Kevin McCarthy agreed."No bribery, no extortion, no obstruction of justice, and no abuse of power," he told reporters."Why are we going through this nightmare?"Polling shows Americans are about evenly split on impeaching and removing Trump - and the process has the potential to backfire on Democrats who face re-election in districts won by Trump.On Thursday, Democratic presidential candidate and former New York mayor Michael Bloomberg came out in favor of impeaching Trump, telling "CBS This Morning" that "I was before opposed to it but after looking at all of the evidence, I think yes."Longtime Democratic analyst David Axelrod, who served as president Barack Obama's chief campaign strategist, offered a blunt prediction for the impeachment timetable."The House will impeach @POTUS by the end of the year because what he did warrants it," he tweeted.