India, Oct. 23 -- The former U.S. envoy to Ukraine has testified before the House Intelligence Committee that President Donald Trump proposed to release military aid to Ukraine on condition that his Ukrainian counterpart Volodymyr Zelensky promise to conduct an investigation of former Vice President Joe Biden and his son Hunter Biden.

Biden is the front-runner for the Democratic presidential nomination in 2020, and his son was on the board of a gas company in Ukraine.

In one of the most damaging evidence yet in the Democrats' impeachment inquiry against Trump, Ambassador William Taylor said that he was told the President wanted Ukraine to probe the dealings of Joe Biden, his potential rival in the 2020 presidential election.

"Our relat...