US House Speaker Nancy Pelosi speaks during a press conference on Capitol Hill in Washington D.C., the United States, on Dec. 5, 2019. Nancy Pelosi has greenlighted the drafting of articles of impeachment against President Donald Trump, as the White House braces for a Senate trial.(Photo: Xinhua)

US House Speaker Nancy Pelosi has greenlighted the drafting of articles of impeachment against President Donald Trump, as the White House braces for a Senate trial.

Speaking on Capitol Hill Thursday morning, Pelosi said she is asking the House Judiciary Committee to draft articles of impeachment, accusing Trump of having abused his power for "his own personal political benefit at the expense of our national security."

"The president leaves us no choice but to act," she said.

Trump, who has denied any wrongdoing or a "quid pro quo," renewed his attacks on the months-long impeachment process in a series of tweets.

"The Do Nothing, Radical Left Democrats have just announced that they are going to seek to Impeach me over NOTHING," the president wrote. "This will mean that the beyond important and seldom used act of Impeachment will be used routinely to attack future Presidents."

Claiming "the Republicans have never been more united," he said, "We will win!"

Pelosi's announcement came a day after the House Judiciary Committee chaired by Democrat Jerry Nadler held its first hearing as part of the impeachment proceeding against Trump.

At the hearing marked by partisan disagreements over Trump's conduct toward Ukraine, three constitutional law professors, called by Democrats, testified that they believed Trump committed impeachable offenses.

A fourth legal expert, whom Republicans invited, cautioned the Democrat-led House against moving forward with impeaching the president.

The House Judiciary Committee announced on Thursday that it will hold a second hearing on Monday.

The hearing is "to receive presentations from counsels" to the House intelligence and judiciary panels and lawyers of both parties will be present, according to an announcement.

House Democrats are looking into whether Trump abused his office by pressuring Ukraine into launching investigations that could benefit him politically. Lawmakers are also examining whether the Republican conditioned a White House meeting or a military aid to Ukraine on those probes.

The articles of impeachment under consideration are reportedly abuse of power and bribery, obstruction of Congress, and obstruction of justice.

Polls have shown US voters are also largely divided along party lines over impeachment.

The White House has so far refused to cooperate with the impeachment proceeding, accusing Democrats of an unfair process, but suggested on Thursday that it would likely be part of the Senate trial.

Counselor to the president Kellyanne Conway told reporters at the White House that they are "very ready" for the trial.

The Senate process, she said, "would include live witnesses who have visibility and knowledge into facts." White House counsel Pat Cipollone would likely testify, she added.

According to the nation's constitution, the House shall have the sole "Power of Impeachment" while the Senate shall have the sole "Power to try all impeachments."

Trump will be impeached if the House approves any of the articles of impeachment the House Judiciary Committee has recommended by a simple majority vote.

But conviction can only happen in the Senate and requires at least two-thirds of its members, or 67 senators, to vote in favor. Currently, the Senate has 53 Republicans, 45 Democrats and two independents.

Senate Majority Leader Mitch McConnell on Thursday tweeted criticism of Pelosi, accusing her of advancing a "rushed and partisan impeachment process."

David Axelrod, director of the University of Chicago's Institute of Politics, said in tweets that he believes the House will impeach Trump by the end of the year but the Senate won't convict him.

"Impeachment will eclipse all for the next seven weeks. And then it will recede, and other events will supersede it as the election year moves on," Axelrod predicted.