WASHINGTON, D.C.: Two top US diplomats delivered gripping testimony Wednesday about Donald Trump's efforts to get Ukraine to investigate his potential 2020 rival Joe Biden, as the impeachment inquiry into the president shifted into a new phase of high-stakes televised hearings.

Trump dismissed the probe in the Democratic-led House of Representatives as a 'witch hunt' and said he was 'too busy' to watch the first public hearings, during which he received staunch backing from Republican lawmakers.