WASHINGTON - US President Donald Trump has defended enquiring about his presidential rival Joe Biden during a call with the Ukrainian President Volodymyr Zelensky.
Mr Trump denied pressuring Mr Zelensky to look into unsubstantiated corruption allegations against Mr Biden.
But accusations that Mr Trump abused his power in raising Mr Biden with a foreign leader have pushed more Democrats towards raising impeachment.
A top Democrat said impeaching the president now "may be the only remedy".
Democrats have accused Mr Trump of threatening to withhold a $250m (£200m) aid payment to Ukraine as a means to pressure Mr Zelensky to investigate Mr Biden and his son Hunter.
Mr Trump and his allies have claimed that Mr Biden encouraged the firing of Ukraine's top prosecutor because the prosecutor was investigating a company that employed Hunter Biden - a claim which has never been substatiated.
"Of course it's an impeachable offence," Democratic congressman Jim Himes told CNN of the president's alleged attempt to pressure Ukraine.
"I can't tell you that the House will move into impeachment mode right away, but this really ups the ante," Mr Himes said.
President Trump has not provided any evidence of corruption involving Mr Biden or his son, Hunter, and the former vice-president denies any wrongdoing.
Pressure is growing on Mr Trump to release a transcript of his phone call with Mr Zelensky.(FA)