Joe Biden's standing in the
Democratic presidential nomination battle has slipped in Iowa against top rivals including
Elizabeth Warren, the frontrunner in the early-voting state, who on Friday answered critics over how she will pay for her progressive policies.
As the 2020 protagonists clashed, one of the lower-polling Democratic candidates who started the contest with considerable promise, ex-congressman Beto O'Rourke, announced he was quitting the race.
O'Rourke's exit provided the latest dynamic in the crowded race to see who will challenge US President
Donald Trump in November 2020.