Presidential candidate Sen. Bernie Sanders said on Labor Day, “We honor and respect the millions and millions and millions of men and women who do the hard work that keeps this country going.”

The populist independent senator from Vermont – speaking to reporters ahead of marching in the largest annual Labor Day parade in the first-in-the-nation presidential primary state of New Hampshire – added it’s a day to spotlight “the needs of working families.” Sanders, once again, made his pitch to raise the minimum wage to “a living wage,” gender pay equality, and to make “it easier for workers to be able to join unions.”

Sanders has been making a hard sell for labor support while running a second straight time for the presidential nomination. As he unveiled his “Workplace Democracy” plan last month, he called for doubling union membership and giving workers the right to strike without the fear of their jobs being filled by replacement workers.

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Meanwhile, halfway across the country, former Vice President Joe Biden was greeting voters at the Hawkeye Area Labor Council Labor Day Picnic in Cedar Rapids, Iowa, the state that votes first in the nominating calendar.

The front-runner among the 2020 Democrats promised in an email to supporters that “if I’m elected president, together, we’ll protect and strengthen the right to organize and collectively bargain.”

Biden held the first rally of his latest White House bid at a union hall in Pittsburgh. And, on the campaign trail, the former vice president repeatedly had emphasized his longtime close ties with organized labor.

Biden’s message to union workers this Labor Day: “I’ll never forget the battles you’ve waged and victories you’ve won, and I’ll never forget to stand with you and with labor unions every day.”

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Sen. Elizabeth Warren, the third of the current top-three contenders among the Democrats, said in a message Monday to union members that “the playing field today is tilted against working families, and that is why now, more than ever, America needs a strong labor movement.”

The progressive senator from Massachusetts emphasized, “I’m proud to stand shoulder to shoulder with the labor movement and with working men and women across this country.”

But, while Biden, Sanders, Warren and many of the other candidates have been courting organized labor, unions appeared in no rush to jump in and make endorsements as the record-setting field of Democrats battled for the party’s presidential nomination.

Biden, to date, has been the only candidate to land a major national union endorsement. The International Association of Fire Fighters (IAFF) backed him days after he jumped into the race. The smaller United Electrical, Radio and Machine Workers of America union endorsed Sanders last week.

It’s a switch from four years ago when many of the powerful national unions weighed in early – as most of them backed eventual nominee Hillary Clinton.

This time around, with the White House hopefuls mostly in agreement on union-friendly causes such as the push for a $15-per-hour minimum wage, there’s been less of an incentive for labor to endorse early in the process.

“I think we have a plethora of good candidates. I think the vetting process is much more in-depth this time around than last time around. We only had basically two candidates,” New Hampshire AFL-CIO President Glenn Brackett told Fox News.

A veteran Democratic strategist with close ties to organized labor said some unions were sitting on the sidelines apparently because they’re worried they’ll endorse the wrong candidate.

“No union wants to be the one that steps out and messes up unity at the convention or unity in the party to actually beat Donald Trump,” said the strategist, who asked to remain anonymous to speak more freely.

“It is the culture of this party right now to ‘just win’ and don’t worry about who it is. It needs to be someone more to the center. So, no union wants to step out to endorse somebody further to the left early and create some fight that will, later down the road if Trump is re-elected, be blamed for messing up,” the strategist added.

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While Trump didn’t land any major union endorsements in 2016, he did gain the support of plenty of rank-and-file members. Clinton won the union vote by just 8 percentage points, down from President Barack Obama’s 18-point margin over GOP nominee Mitt Romney in the 2012 election.

But, Brackett said he thought Trump’s in for a rude awakening in 2020, telling Fox News the president “blew a lot of smoke and a lot of people believed him. And, I think after the last three years of seeing his behavior, I don’t think he’s going to enjoy the same dept of support from union members that he did in the last election. I think he’s in for a big surprise this time around.”