Former VP says US president has 'betrayed his nation,' marking a much tougher stance from Democratic White House hopeful who is now neck and neck with Elizabeth Warren in race

Democrats demand documents from administration officials, including vice president, as Trump disparages investigation, refuses to cooperate

US vice president, a key intermediary between White House and Ukraine, has until now rarely been drawn into Trump controversies

US president lashes out as Democratic-led House moves ahead with its inquiry into abuse of power; civil war tweet draws condemnation from Republican lawmaker

US president says he 'deserves' to meet intelligence officer whose complaint sparked impeachment probe; accuses leader of congressional inquiry of 'treason'

Incendiary complaint says Trump administration scrambled to 'lock down' records of phone conversation in which president pressed for Ukraine to probe Biden

After US president implies those who helped his accuser should be executed, Democratic House committee chairman warns him against 'witness intimidation'

White House allegedly tried to cover up details of president's phone call; intelligence chief Joseph Maguire calls whistleblower complaint 'unprecedented' amid impeachment calls

Dramatic switch by swing district Democrats who are veterans of national security community signals how much the political climate has changed in the last week

'I didn't do it, I didn't threaten anybody. No push, no pressure, nothing,' US president tells reporters a day after Democrats announce the launch of proceedings against him