In phone call central to impeachment inquiry, US president asked Volodymyr Zelensky 'to do us a favor,' said 'there's a lot of talk about Biden's son'

Pelosi and rookie Congress members with national security backgrounds get behind formal impeachment proceedings despite risk to some closely fought districts

US president says July phone call with newly elected Zelensky focused on Ukrainian corruption; he cited the former US veep and his son, a local gas company board member, as example

US president reportedly turned to Ukrainian leader Volodymyr Zelensky in bid to piece together a corruption complaint against Joe Biden ahead of 2020 race