Every previous winning presidential candidate — and a good number of losing ones like John McCain and John Kerry — have been popular. Even Bill Clinton, who kind of limped into office with 43 percent of the popular vote in 1992, enjoyed approval ratings in the mid-to-high 60s during his post-election winter.

Donald Trump is not like that. While Barack Obama won the votes of a decent number of people who also had a favorable impression of McCain, Trump triumphed in the face of a badly divided opposition. Perhaps his most impressive political feat was trouncing Hillary Clinton 47-30 among the 18 percent voters who viewed both candidates negatively. He got 17 percent of the vote of people who said he wasn’t qualified to serve as president, 19 percent of the vote of people who said he lacked the temperament to be president, and 23 percent of the vote of people who wanted the next president to be more liberal than Obama.

A normal person would have responded to this kind of strange victory with some sort of effort to reassure people or shore up his support. But rather than pivot or mature, Trump spent his transition months feuding with the intelligence community, offered the most divisive inaugural address in memory, and then on his first full day in office went to Langley to deliver what amounted to a campaign rally in front of the CIA’s Memorial Wall.

These antics have taken Trump much further than anyone predicted they possibly could, and so he evidently has no intention of abandoning them. But in parallel on Saturday, millions of people took to the streets in cities and towns around the country to do the one thing his opponents never really did during the campaign — take the prospect of a Trump administration seriously. After benefitting mightily from a fractured opposition that systematically underestimated his candidacy, Trump is now finally in for the fight of his life.

Donald Trump won because nobody thought he could

Donald Trump won 46 percent of the popular vote on the way to victory — a victory driven by capturing the electoral votes of seven states in which he failed to capture a majority of the vote: Wisconsin, Michigan, Pennsylvania, North Carolina, Florida, Arizona, and Utah.

He was elected anyway because many people who didn’t want him to be president couldn’t bring themselves to vote for his opponent. Some of that was her own fault. But some of it was because Trump, in an odd way, was the beneficiary of the perception that he couldn’t possibly win.

People who felt he’d be a bad president felt secure in dissenting from the Democratic Party to either the right (Gary Johnson) or the left (Jill Stein) because everyone knew Clinton would win anyway. Almost everyone who had any kind of serious policy doubts about Clinton invested vast time and energy in exploring them, regardless of whether or not they had much more profound doubts about Trump, because everyone knew Clinton would win anyway. Mainstream journalists spent more time poring over potential access-seeking at Clinton’s undoubtedly life-saving charitable foundation than they did detailing the fact that Trump’s foundation was a potentially criminal fraud that appears to have had no legitimate public benefit.

Everyone knew Clinton would win anyway.

That was, obviously, a miscalculation. But it’s important to be clear about what the miscalculation was. Trump’s opponents failed to unify around a single compelling alternative. He wasn’t popular on Election Day and he wasn’t popular on Inauguration Day. And he’s not doing anything to try to turn that around.

Trump is in for the fight of his life

Like any sensible pundit looking back on 2016, I am getting out of the political predictions game. But what we saw in Saturday’s demonstrations is that nobody is taking Trump’s defeat for granted anymore. The women and men who marched in cities and towns all across the country undoubtedly have different opinions about taxes and foreign policy and government email server protocol and single-payer health care and bank regulation. They agree that Trump is alarming and that it is incumbent upon them, personally, to try to come together and do something about it.

The absence of that kind of attitude among the 54 percent of Americans who didn’t vote for him last November is one of the primary reasons he was able to win.

Now that it is present, he has lost one of his main advantages.

Trump is a president who is in many ways unusually vulnerable to protest. He’s not a policy wonk who has the disposition to tune out the street theater and focus on issues. And his policy agenda, as far as we can tell, consists largely of unpopular causes like cutting taxes on millionaires, deregulating banks, and stripping millions of their health insurance. His administration’s first policy action was to prevent homeowners from getting a small scheduled mortgage discount.

He’s also a president who is uniquely vulnerable due to his conflicts of interest. Past wealthy presidents have held their assets in diversified funds managed by blind trusts in part to avoid corruption. And his conflicts run both ways — a non-corrupt president wouldn’t want his political adversaries to be able to use his private business interests against him. Million-person mass demonstrations can’t be done every day. But even relatively small-scale demonstrations and acts of civil disobedience targeting Trump-branded hotels, golf courses, office buildings, and apartments can be dramatic and telling.

The need for law enforcement officials to be perpetually intervening to safeguard Trump’s personal financial interests will dramatize the corrupt nature of the setup in a more profound way than any number of preachy ethics documents. Protests could also potentially create the legal standing necessary to raise questions about the validity of Trump’s lease at the Old Post Office and the emoluments clause.

The specter of Vladimir Putin has loomed, at times literally, over much liberal thinking about Trump’s victory. But Putin didn’t trample Russia’s democratic norms. Russia simply never had any to begin with. And Barack Obama was no Boris Yeltsin. The country he bequeathed to Trump has its share of problems, but it simply isn’t the broken, bankrupt, “American carnage” depicted in Trump’s inaugural address. He won because people didn’t take the threat of him winning — or if him trying to govern as he campaigned — seriously enough to go out and stop him.

This weekend, that ended.

Watch: Millions joined pro-women, anti-Trump rallies