When the Democratic Party has a debate in Detroit, of all cities, you might think that labor unions would be mentioned. Right?
But CNN was hosting these debates, and CNN sucks.

But moderators did not ask those questions. In fact, they didn’t ask a single candidate about the national decline in union membership. They didn’t ask candidates what they’d do to make sure low-wage and gig workers could form unions. They could have asked candidates about the Workplace Democracy Act. Introduced by Sanders and co-sponsored by Warren, Harris, Gillibrand, and Booker, the bill would repeal right-to-work laws. Or the PRO Act, which would expand bargaining rights, and which was co-sponsored by Ryan in the House and by Warren, Harris, Gillibrand, Booker, Sanders, and Michael Bennet in the Senate. When Jake Tapper did mention unions on Tuesday, it was to ask Bernie Sanders to respond to a criticism levied by Tim Ryan: that Medicare for All would deprive union members of the private plans guaranteed by their contracts. Wednesday’s debate was even worse. When unions did get a mention, it was only because a candidate decided to bring them up.

“Their broad statements of solidarity are not enough,” Henry, SEIU’s president, told New York before Tuesday’s debate got underway. Unions, she added, wanted “concrete” plans. On Twitter, AFL-CIO president Richard Trumka issued a similar warning

The Dems dominated Congress from 1932 to 1994, mostly because of union support.
Then came Bill Clinton and NAFTA.
NAFTA was a Republican FTA, and a majority of Dems in Congress voted against it, but the leader of the Democrats had betrayed unions and so union voters failed to turn out in the next election.
Or any election since then.

Since 1994, Democratic candidates have said all of the things that unions wanted to hear in the primaries, but then quickly turn their backs on unions after the elections.
This time around is no different.
So the real question is "Which candidate is just blowing smoke? And which candidate is for real?"

The AFLCIO rating isn't the best way to measure authenticity. It just gets you in the ballpark.
Fortunately, In These Times has a detailed breakdown of each candidate.

Some candidates are predictably awful.

In May, Biden held a fundraiser at the Los Angeles home of a board member of Kaiser Foundation Hospitals, a subsidiary of healthcare giant Kaiser Permanente. The National Union of Healthcare Workers (NUHW), which has a longstanding dispute with Kaiser in California over mental health staffing levels, called on Biden to cancel the event. They never heard back, says NUHW President Sal Rosselli. NUHW members protested outside the house, but Biden “went into the event and didn’t even talk to our folks,” Rosselli says. “That’s very disappointing.”

Biden also didn’t endear himself to the labor movement by voting for NAFTA and supporting the Trans-Pacific Partnership (TPP) trade agreement, both of which unions opposed.

Some candidates are predictably good.

In contrast, the leading presidential candidates from the Senate have been out front on labor law reform. Sanders has been pushing the Workplace Democracy Act (WDA) for decades (beginning as a congressman in 1992), which is co-sponsored by Booker, Harris and Warren. The WDA can be seen as a forerunner of the PRO Act; it also legalizes secondary boycotting, stops companies from delaying a first contract with workers and gives bargaining rights to many workers who are currently classified as independent contractors. (Unlike the PRO Act, it would let all workers unionize via card check as a matter of course.) Sanders’ method has been persistence: He reintroduced the WDA throughout the 1990s in the House, then brought new versions into the Senate in 2015 and 2018. As with other issues, such as Medicare for All, the Democratic Party has now caught up to him.

It took Sanders years to earn the backing of any national union. They didn’t flock to him when he first ran for Congress in 1988, but came around after he won congressional campaigns in the early 1990s.

But a few candidates are surprisingly solid on labor unions.

Elizabeth Warren doesn't have the track record of Bernie, but she is on record for a very unique bill that I fully support.

Warren’s Accountable Capitalism Act is a good example. Introduced in the Senate in 2018, the bill would empower employees to elect at least 40% of board members at large U.S. companies. This new board could then (in theory) push management to do something about yawning pay disparities between the C-suite and average workers.

This is one of the only instances in which Bernie copied Warren (in May 2019), rather than the other way around.
Mayor Pete Buttigieg is one of the last people I would suspect of having pro-union credentials.

Buttigieg, for example, has been in tune with the building trades unions in South Bend. “He’s been fantastic,” says Jim Gardner, business representative of the Operating Engineers Local 150. Buttigieg spoke out against repealing the common construction wage and backed a “responsible bidding” city ordinance that requires any company bidding on a city contract to reveal OSHA violations, Gardner says.

Mayor Pete has also proposed one of the most sweeping pro-union bills so far.

Kamala Harris has deep ties to California unions, although no significant track record for anything bold.
After that things go downhill fast.

O’Rourke’s voting record in Congress was more conservative than the average Democrat’s. He has backed easing regulations on Wall Street and raising the eligibility age for Social Security.

Booker’s current stance on labor and workers’ rights is solidly progressive (relative to the other leading candidates), but he has a bit of an Achilles’ heel: his longstanding support for school vouchers and the charter school movement in Newark, N.J., where he was a city council member and mayor.

Even Bloomberg admits that we need stronger unions.