"I Voted" stickers cover a table at a polling station during the North Carolina primary on Super Tuesday in Charlotte, North…
"I Voted" stickers cover a table at a polling station during the North Carolina primary on Super Tuesday in Charlotte, North Carolina, March 3, 2020.

WASHINGTON - Six more U.S. states vote next Tuesday in the marathon chase for the Democratic presidential nomination, with the two remaining key candidates, former Vice President Joe Biden and Vermont Sen. Bernie Sanders, dueling to gain an edge.

"I like Joe Biden. I think he's a decent human being," Sanders said Wednesday. "But we have a very different vision for this country. Joe has his ideas about the future, and I have mine."

Among other issues, the two widely differ on U.S. health care, with Sanders calling for a government-run system and an end to the use of private insurance plans to pay health care expenses. Meanwhile, Biden wants to make improvements in the Affordable Care Act that now controls health care spending in the United States.

Next up on the political calendar are party primaries in the Midwestern states of Michigan and Missouri, the western states of Washington and Idaho, and Mississippi in the South, with caucuses in the upper Midwest state of North Dakota. Democrats living abroad are also voting in a collective primary that has already started and ends March 10.

Democratic presidential candidate former Vice President Joe Biden speaks at a primary election night campaign rally in Los Angeles with his wife Jill Biden, left, and his sister Valerie, March 3, 2020.

After 14 states voted Tuesday, Biden, a three-decades-long pillar of center-left politics in the Democratic Party, and Sanders, a self-declared democratic socialist long at odds with many in his party, were left as the key challengers to face Republican President Donald Trump in next November's national election.

Biden won 10 of the 14 states at stake in the Super Tuesday voting, with Sanders taking four.

In next week's face-off, the fivethirtyeight.com political forecasting site says that Sanders is favored in Michigan and Washington, the two states with the largest number of delegates at stake to attend the party's national convention in July, as well as in Idaho and North Dakota, and among Democrats living in other countries. Biden is favored in Missouri and Mississippi.

But if nothing else, the last week of voting shows that pre-election forecasts are an iffy proposition, at best.

Before winning last Saturday's Democratic primary in South Carolina, Biden's chances had been all but written off.

He had been trounced in the first three nominating contests in February. And in three tries for the presidency over three decades, he had yet to win a single state presidential nominating contest on his own behalf. He eventually served eight years as vice president under former President Barack Obama.

Then came Biden's decisive victory in South Carolina and more wins on Tuesday. Obama has not endorsed anyone in the nominating race.

Obama factor

The direct one-on-one contest between Sanders and Biden started almost immediately.

The Sanders campaign released a television ad in Florida, which votes March 17, showing the former president praising Sanders.

Democratic presidential candidate Sen. Bernie Sanders, I-Vt., speaks during a primary night election rally in Essex Junction, Vt., March 3, 2020.

"Bernie is somebody who has the virtue of saying exactly what he believes, great authenticity, great passion and is fearless," Obama says in the ad. "Bernie served on the Veterans' Affairs Committee and got bills done. I think people are ready for a call to action. They want honest leadership, someone who cares about them. They want somebody who's going to fight for them, and they will find that in Bernie."

The ad concludes with Obama saying: "That's right, feel the 'Bern.'"

The Biden campaign disputed the suggestion that Obama is supporting Sanders.

"Barack Obama chose Vice President Biden to be his partner over eight years in the White House, entrusting him with managing the stimulus that saved our economy from a Depression, obtaining the deciding vote for the Affordable Care Act, and countless national security priorities," the Biden campaign said. "By contrast, Sen. Sanders explored a primary challenge to President Obama (in 2012), who he compared to a 'moderate Republican' and said was not a 'progressive.'"

The Biden campaign concluded, "As recent history has proven, no quantity of ads can rewrite history — and there's no substitute for genuinely having the back of the best president of our lifetimes."