US Democrats have opened a formal impeachment inquiry into President Donald Trump over allegations he sought help from a foreign power to damage a political rival.
Top Democrat Nancy Pelosi said the president “must be held accountable”.
Mr Trump denies impropriety and called the efforts “witch hunt garbage”, while also claiming it would help his re-election chances in 2020.
While there is strong support from Democrats on impeachment, if the inquiry moves forward it is unlikely to pass the Republican-controlled Senate.
The dramatic move, the first step in a complex process that stands little chance of driving Trump from office, pushed US politics into a perilous new chapter just 14 months before new elections for control of the White House and Congress.
The row was sparked by reports an intelligence whistleblower lodged a formal complaint about a phone call President Trump made with Ukrainian counterpart Volodymyr Zelensky.
Trump has admitted discussing Biden with Zelensky, but denies he tied hundreds of millions of dollars in aid to Kiev to it investigating the former US vice president.
On Tuesday the US leader said he had frozen aid to Ukraine, but only to force European allies to increase their own support for Zelensky’s government.