US Democrats have opened a formal impeachment inquiry into President Donald Trump over claims that he sought political help from Ukraine.
The decision by top Democrat Nancy Pelosi follows growing demands from her party. She said the president “must be held accountable”.
Mr Trump has denied impropriety and argued that impeachment would be politically “positive” for him.
No US president has ever been removed from office by impeachment.
There is widespread support among Democrats in the lower house for impeachment, more than 145 out of 235 members are in favour.
But if impeachment moves forward it is unlikely to pass the Republican-controlled Senate and opinion polls show it is unpopular among US voters.
Last week reports said US intelligence officials had complained to a government watchdog about Mr Trump’s interactions with a foreign leader, who was later revealed to be the president of Ukraine, Volodymyr Zelensky.
That whistleblower’s complaint, deemed “urgent” and credible by the intelligence inspector general, has been demanded by Democrats but the White House and Department of Justice have refused to provide it.
What exactly was said remains unclear but Democrats accuse Mr Trump of threatening to withhold military aid to force Ukraine to investigate corruption allegations against Mr Biden and his son Hunter.
Mr Trump has acknowledged discussing Joe Biden with Mr Zelensky but said he was only trying to get Europe to step up assistance by threatening to withhold military aid.