DETROIT (REUTERS) - Joe Biden made a last-minute pitch on Tuesday (March 10) to the blue-collar workers he hopes will help deliver a critical win in Michigan's Democratic presidential primary, as rival Bernie Sanders aims for an upset that would revive his flagging White House hopes.

Voters in Michigan and five other states were making their choice in a two-man battle for the right to face Republican Donald Trump in November - between Biden, the former vice president who has run as a moderate, and Sanders, a democratic socialist and US senator from Vermont who has become the standard-bearer for the party's left flank.

Biden's impressive showing in last week's "Super Tuesday" states, along with a surge of endorsements and campaign donations, has elevated him to front-runner status, narrowing Sanders' path to the nomination.

The most important vote on Tuesday was in Michigan, the cradle of America's auto industry where Sanders sprang a stunning 2016 upset over Hillary Clinton that ensured a long nominating fight - something Biden hopes to avoid this time.

Washington, Mississippi, Missouri, North Dakota and Idaho also hold contests.

Michigan is also likely to be a crucial battleground in the general election, after Trump became the first Republican presidential candidate four years ago to carry the state in nearly three decades.

Late in the day, both candidates called off planned rallies in Cleveland, Ohio, on Tuesday due to concerns over the coronavirus outbreak, which has rattled markets and prompted Democrats to criticize the Trump administration's response.

The campaigns said they were following guidance from Ohio public health officials. Until now, Democratic candidates as well as Trump have largely continued to hold large-scale events despite the epidemic.

'HAVE TO BE PRACTICAL'

Biden, who has touted the Obama administration's decision to bail out the auto industry, made a morning campaign stop at Detroit's first new auto assembly plant in decades, owned by Fiat Chrysler Automobiles.

"Unions built the country," Biden said, yelling through a bullhorn. "You're the best damn workers in the world."

But his visit was marred by a clash with one worker who suggested he planned to confiscate Americans' guns. Biden, whose propensity to veer off script occasionally causes self-inflicted wounds, snapped at the worker with an obscenity.

Michigan is emblematic of the country's struggle to retain manufacturing jobs.

Sanders has attacked Biden for supporting international trade deals like the North American Free Trade Agreement, which is unpopular among many of Michigan's workers.

As Biden left the plant, video showed some workers chanting "Trump!"

In Detroit, Josh Greenwood, 48, said he voted for Sanders on Tuesday because he is the "complete opposite" of Trump, while Biden's record is questionable.

"He's also really a Republican in my view," Greenwood, who owns a downtown coffee shop, said of Biden. "His voting record shows that he's voted against all of his party's interests for his entire career."

Melissa El-Johnson, a 66-year-old lawyer from Detroit, said she voted for Sanders because Biden would not make "brave, bold decisions" as president.

"He will play it safe, and go along with the old boys club, and this country really needs someone who is going to be willing to make courageous decisions," El-Johnson said. "Bernie Sanders will do that."

But other voters said Biden would offer a steady hand in volatile times and had better odds of defeating Trump.

"We all have to be practical in our choices, and not emotional," said Sameerah Saadiq, 38, the owner of an early childhood education center, who had initially supported Sanders but flipped to Biden after his Super Tuesday victories.

"Bernie would definitely be an emotional choice for me. Biden is more sober in his positions."

BIDEN EYES KNOCKOUT BLOW

Michigan, with 125 delegates, is the largest prize of the six states voting on Tuesday, when a total of 352 delegates to July's Democratic convention will be up for grabs.

Since last week's romps, Biden has roared into the national lead in polling and delegates, knocked out his remaining viable rivals except Sanders and swept up another wave of endorsements from prominent Democrats and former rivals such as Senators Kamala Harris and Cory Booker.

Biden has a double-digit lead in the four most recent polls taken in Michigan. But Clinton held a similar polling lead in Michigan over Sanders, a senator from Vermont, before the 2016 primary.

Biden, whose victories in South Carolina and on Super Tuesday were powered by strong support among black voters, hopes to receive a similar boost on Tuesday. In 2016, about one-fifth of Democratic primary voters in Michigan and Missouri, and an overwhelming 70% in Mississippi, were black.

A Biden breakthrough in Michigan, and big victories in Missouri and Mississippi, where he is heavily favored, could prove too much for Sanders to overcome. By the end of March, about two-thirds of the delegates up for grabs will be allocated.