Former Sen. Al Franken, D-Minnesota, now wishes he would not have resigned his seat over sexual assault allegations in 2018. (Tom Brenner/The New York Times)

At least three 2020 Democratic presidential candidates have learned in recent days that it's one thing to promise pie in the sky but another to deliver on it.

Sen. Bernie Sanders, I-Vermont, realized his $15 minimum wage plan doesn't work so well for his campaign staff. Former Vice President Joe Biden admitted he couldn't repeat the lie his boss did in promising that health care consumers could keep their doctors under his plan. And Sen. Kirsten Gillibrand, D-New York, felt heat when it was revealed her crowning #MeToo moment left some of her far left colleagues with heartburn.

Beginning in May, some Sanders staffers quietly began pointing out the hypocrisy of trying to sell the public on a uniform $15 minimum wage when they weren't receiving such an amount. However, Sanders' campaign staff disagreed and dismissed the demand until a field worker recently spilled the beans to The Washington Post.

Privately, according to reports, the senator fumed that some jobs weren't worth $15 an hour, which certainly was true for the workers, who were a small step above volunteers. He also whined that "people are going outside of the process and going to the media. That is really not acceptable. It is really not what labor negotiations are about, and it's improper."

Except, of course, when they're telling on big corporations.

On Tuesday, though, Sanders relented and said he'd pay his field organizers $15 an hour, but he also cut the the number of hours a week they could work.

Throughout the country, $15 minimum wage opponents were saying, "Told ya."

Biden, happy to defend former President Barack Obama's lies about consumers keeping their health plan and their doctor when the Affordable Care Act was rolled out almost a decade ago, realized his plan would no more let them do that than the former president's did.

"Well look," he told the Washington Examiner, "I can't promise — I can promise them that if in fact the private insurance they have is kept by their company, they keep whoever that plan allows. That's all I can promise."

Biden's plan, unlike the Medicare for All plans of many other candidates, wants to build on what became known as Obamacare but add a "public health insurance option" that functions similar to Medicare and Medicaid.

His plan is estimated to cost $750 billion over the first 10 years compared to a sticker price of $30 million to $40 million for Medicare for All plans.

But before the plan was announced last week, Biden told AARP voters in Iowa, "If you like your health care plan, your employer-based plan, you can keep it," and "if you like your private insurance, you can keep it."

The Affordable Care Act never could allow such, which Obama knew when he said it, because many of the then-current plans didn't meet the program's strict guidelines. And, so, eventually, millions of consumer plans were canceled.

Meanwhile, Gillibrand, currently at 0.6% in the polls, was swarmed by media outlets after former Sen. Al Franken, D-Minnesota, and a number of senators recently told the New Yorker they regretted Franken's decision to resign after sexual abuse charges were made against him in early 2018.

"Oh, yeah," Franken said when asked if he regretted his decision. "Absolutely."

Suggesting he step down without getting all the facts is "one of the biggest mistakes I've made" in 45 years in the Senate, said Sen. Patrick Leahy, D-Vermont.

"If there's one decision I've made that I would take back," said former Sen. Heidi Heitkamp, D-North Dakota, "it's the decision to call for his resignation."

Well, sniffed Gillibrand, it was Franken's decision to step down.

No doubt it was, but she — in the midst of assorted #MeToo allegations across the country — was the first lawmaker to step out and suggest he resign before the Senate Select Committee on Ethics could make a judgment on his status.

"It's his decision and his alone whether to wait out his ethics committee hearing, whether to wait for his next election," she said. "The decision I made was whether or not to carry his water and stay silent. And given eight allegations, two since he was senator, and the eighth one being a congressional staffer, I couldn't stay silent."

In losing Franken, Democrats lost a particularly vicious barb for President Donald Trump, and even a potential 2020 opponent. The former "Saturday Night Live" comedian was never shy about expressing his opinion — whether it had any truth in it or not — while his replacement, a reliable Democrat nonetheless, is less candid with her comments.

As the campaign rolls on, it won't be surprising to see other 2020 Democratic hopefuls come face to face with the reality of their stances and suddenly learn how to backpedal.