What is at stake in all of this is nothing less than our democracy.

WASHINGTON (AFP) — A deeply divided Congress formally opened a new, public phase of its investigation into Donald Trump on Thursday as US lawmakers voted for the first time to advance the impeachment process targeting the US president.

“Today the House takes the next step forward as we establish the procedures for open hearings… so that the public can see the facts for themselves,” said House Speaker Nancy Pelosi, Washington’s top Democrat.

“What is at stake in all of this is nothing less than our democracy.”

The House of Representatives voted along party lines, 232 to 196, to pass a resolution that lays out guidelines for the next stages of the impeachment process.

All Republicans opposed the measure, despite agitating for weeks for such a vote that could end the secretive depositions and bring the process into the open.

Democrats are seeking to learn whether Trump abused his presidential power by pressuring a foreign government to investigate a domestic political rival.

Trump has repeatedly branded the inquiry as illegitimate and politically motivated, and he was true to form in his instant reaction to the vote.

“The Greatest Witch Hunt In American History!” he boomed on Twitter.

The White House accused opposition Democrats of being “fundamentally un-American” in their “unhinged obsession with this illegitimate impeachment.”

“Democrats are choosing every day to waste time on a sham impeachment — a blatantly partisan attempt to destroy the President,” Press Secretary Stephanie Grisham said in the statement after the vote.

Trump meanwhile called on his fellow Republicans to rally behind him even as he faced the embarrassing likelihood of becoming the third president in history to be impeached and placed on trial for removal in the Senate, over an alleged scheme to extort Ukraine’s help to get him reelected in 2020.

The embattled president retweeted a rallying cry from Fox News host Laura Ingraham that called on Republicans to “stand together and defend the leader of their party against these smears.”