Joe Biden and Bernie Sanders on Saturday 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 for the first time since the field narrowed to two credible candidates.

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

Standing on an outdoor stage on a sunny day in St. Louis, at times wearing his signature aviator sunglasses, the politically moderate Biden savored his spectacular revival in the race for the White House.

“What a difference a day makes,” he exulted. “This time last week I was in South Carolina and the press and the pundits had declared Biden’s campaign dead.”

“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.”

With the monumental Gateway Arch — a symbolic entryway to the American West — in the background, the former vice president mentioned Sanders only indirectly.

Biden, having gained key backing from erstwhile rivals Pete Buttigieg, Amy Klobuchar and Michael Bloomberg, 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 to an equally enthusiastic crowd in Chicago, underlined his differences with Biden, without directly attacking him.

“Joe Biden is a friend,” he said. “I have known him for many years. But we have records, we have a different vision. The American people will hear about it.”

With the primary now “down to two people,” the progressive Vermont senator said, “it is important for the American people to understand the differences between us — in terms of our record, in terms of our vision for the future.”

Sanders is a democratic socialist who wears his uncompromising positions — government-run health care for all, higher taxes on the wealthy and free university tuition — proudly on his sleeve.

Biden is a centrist who prides himself on his ability to work with Republicans. He is more middle-of-the-road on key issues like health care, where he favors expanding existing insurance programs, and less punitive additional taxes on the wealthy.

At a later rally in Flint, Michigan, Sanders focused on the “real differences” he has with Biden.

These include what Sanders says is Biden’s support for bad trade deals that cost the United States “over 4 million good-paying jobs.”

“I stood with the unions, the working families of this country” and voted against the trade deals, Sanders said.

The Vermont senator also blasted Biden for voting in favor of the Iraq conflict. “I led the opposition to the war in Iraq,” Sanders said.

Amy McDowell, 40, who was at the rally, said after South Carolina and the numerous endorsements for Biden, “I feel like we can see exactly who the establishment is comfortable with.”

Can Sanders win on Tuesday in Michigan? “You know, we’ve got a war to fight. But I still think Bernie has the support of his people,” she said.

In addition to Michigan — the biggest prize — and Missouri, Idaho, Mississippi, North Dakota, and Washington state hold Democratic primaries on Tuesday.

Illinois, where Sanders first spoke, does not hold its primary until March 17, two days after the next Democratic debate, to be held in Phoenix, Arizona.

Hawaii congresswoman Tulsi Gabbard is still on Democratic ballots, but trails so badly that she has not qualified for the debate.

That would leave Sanders and Biden in their first head-to-head encounter of the long campaign season.