New phase as Democrats gear up for two-horse race

Joe Biden and Bernie Sanders have began what amounts to a fresh campaign for the Democratic nomination for president, as the septuagenarians prepare to go head-to-head at the polls.

Biden, the 77-year-old former US vice president, spoke to a large crowd of supporters in Missouri, one of six states that will hold Democratic primaries tomorrow, one week after the Super Tuesday elections brought about a dramatic reversal of fortunes in his favor.

"This time last week I was in South Carolina and the press and the pundits had declared Biden's campaign dead," Biden said in St Louis.

"But South Carolina had something to say about that, and then came Super Tuesday. And today there are 11 victories behind us and we're leading both in delegates and national votes."

Biden mentioned Sanders, 78, only indirectly. Having gained key backing from erstwhile rivals Pete Buttigieg, Amy Klobuchar and Michael Bloomberg, Biden said he was best positioned to "unite this party," promising not to turn "this primary into a campaign of negative attacks."

"That will only re-elect Donald Trump if we go that route," he said.

Sanders, speaking in Chicago, underlined his differences with Biden, without directly attacking him.

At a later rally in Michigan, Sanders - an advocate of government-run health care for all, higher taxes on the wealthy and free university tuition - criticized Biden's support for bad trade deals that cost the United States four million good-paying jobs.