As summer ends and the race for the 2020
Democratic U.S. presidential nomination shifts into a higher gear, former Vice President Joe Biden's perilous position atop the vast field stands to be tested under even more pressure.
Biden, 76, has consistently maintained a comfortable lead over his rivals.
Labor Day serves as the traditional marker for the
White House race to intensify, with five months to go until the first nominating contest - February in Iowa - in the state-by-state process of picking the party's nominee to challenge
Republican President
Donald Trump in the November 2020 election.