WASHINGTON (AP) — House Speaker Nancy Pelosi launched a formal impeachment inquiry against President Donald Trump on Tuesday, acquiescing to mounting pressure from fellow Democrats and plunging a deeply divided nation into an election year clash between Congress and the commander in chief.

The probe centers on whether Trump abused his presidential powers and sought help from a foreign government for his reelection. Pelosi said such actions would mark a “betrayal of his oath of office” and declared: “No one is above the law.”

Pelosi’s brief statement capped a frenetic stretch on Capitol Hill, as details of a classified whistleblower complaint about Trump burst into the open and momentum shifted swiftly toward an impeachment probe. The charge was led by several moderate Democratic lawmakers from political swing districts, many of them with national security backgrounds and serving in Congress for the first time.

After more than two and one-half years of sharp Democratic criticism of Trump, the formal impeachment quest sets up the party’s most urgent and consequential confrontation with a president who thrives on combat — and injects deep uncertainty in the 2020 White House race. Trump has all but dared Democrats to take this step, confident that the specter of impeachment led by the opposition party would bolster his political support

Trump, who was meeting with world leaders at the United Nations, previewed his defense in an all-caps tweet: “PRESIDENTIAL HARRASSMENT!”

Pelosi had barely finished speaking as he began a mini-blizzard of tweets assailing her announcement.

At issue are Trump’s actions with Ukraine. In a summer phone call with Ukraine President Volodymyr Zelenskiy, he is said to have asked for help investigating Democrat Joe Biden and his son Hunter. In the days before the call, Trump ordered advisers to freeze $400 million in military aid for Ukraine — prompting speculation that he was holding out the money as leverage for information on the Bidens. Trump has denied that charge, but acknowledged he blocked the funds.

Ahead of Pelosi’s announcement, Trump authorized the release of a transcript of his call with Ukraine’s president, predicting it would show no evidence of wrongdoing. The transcript is to be made public on Wednesday.

“You will see it was a very friendly and totally appropriate call,” Trump said.