There was a time, not too long ago – the iPhone, Facebook and Twitter all existed – when the two leading Democratic candidates for president of the United States didn’t support the right of gay people to marry.

“I believe marriage is between a man and a woman. I am not in favor of gay marriage,” that inspiring tribune of hope and change, Barack Obama, declared in 2008. His rival, Hillary Clinton, concurred. Gay people shouldn’t be able to marry.

By 2012, Obama backed same-sex marriage. Clinton followed suit, later than most Democrats, in 2013. Three years later, when she would run for president again, there was not a leading Democrat anywhere – name a city, a county – who didn’t support same-sex marriage.

Single-payer healthcare, thanks to Bernie Sanders, may be the new gay marriage.

Once radical and taboo in mainstream Democratic circles, endorsing universal healthcare coverage is now de rigueur for anyone who seriously wants to run for president on the Democratic side in 2020. Kamala Harris, the California senator who seemed to be taking the Clinton route to the nomination by courting her Hamptons donors, is now co-sponsoring Sanders’ Medicare for All bill.

There are 16 Democratic senators supporting the bill, a remarkable number considering where the healthcare debate was two years ago, when Sanders first campaigned for president as a democratic socialist long shot. At the time, pundits, political operatives and countless elected officials dismissed the single-payer Sanders dream as a disingenuous moonshot.

Now, the man who told Obama to lay off Bain Capital (Cory Booker) and the woman who once voted in favor of withholding federal funds from sanctuary cities (Kirsten Gillibrand) are co-sponsors of Sanders’ bill. Times, indeed, have changed.

Sanders is an unusual politician because he’s been willing to lead on an issue before its broad popularity was established. For decades, he has roamed the political wilderness crying out for European or Canadian-style single-payer healthcare. He has done it through Democratic and Republican administrations, no matter the electorate’s political orientation at any given time. It is something he believes in.

But most politicians, as gay marriage proved, have few firmly held convictions beyond what they assume the public expects of them. If the people seem to cry out for war, we go to Iraq. If enough people say marriage is between a man and a woman, it stays that way. Few politicians are willing defy conventional wisdom. Politics is a game of self-preservation. Polls determine values.

The movement towards single-payer is humane and sensible. It is also a reflection of the changing zeitgeist and the power of the Sanders movement, which represents the future of the party. As the nation’s most well-liked politician and the hero of millennials, he is now the ringmaster. Clinton’s bitter book tour, if anything, is an affirmation of this.

No one should discount just how arduous the road ahead remains. Single-payer would substantially disrupt our current system, now arrayed around employer-based health insurance. It’s an expensive and inefficient system, but there are people who like the health coverage offered by their employers.

Taxes would rise as healthcare costs are shifted over to the government. This is a trade-off other industrialized countries are willing to make – they also pay their doctors less – but one Americans aren’t used to. Mustering political will to eventually pass such legislation will be another Herculean challenge, as Obamacare was in 2010.

There is an argument, valid in its own way, that the safer approach is to just repair Obamacare. Offer a public option to compete with private insurers. Increase subsidies. Watch premiums fall, insurance companies cry.

Yet a party so moribund as the Democrats needs a worthwhile goal, and single-payer is it. There should be others, like a massive jobs program to halt the erosion of stable work that automation and globalization is killing for good.

In the meantime, freeing healthcare from the clutches of predatory insurance companies is what all Democrats should be thinking about. Better to have Democratic groupthink about guaranteeing healthcare than going to war or keeping people from getting married.