The last four presidents — Bill Clinton, George W. Bush, Barack Obama and Donald Trump — are four very different politicians. But they have one crucial similarity: They all tried to appeal to voters who weren’t obvious supporters.

Clinton promised a “third way,” distinct from traditional Democratic or Republican policies. Bush ran on compassionate conservatism. Obama said that red and blue America shared more in common than pundits claimed.

Even Trump, radical as he is, flouted Republican orthodoxy by sounding like a populist Democrat on Social Security, Medicare and trade. Polls showed that voters judged Trump to be more moderate than any Republican nominee since the 1970s.

The art of peeling off voters — those in the middle or those who aren’t ideological — may be the most important skill in politics. It doesn’t require a mushy centrist policy agenda, either. Trump has made that clear. So, in earlier eras, did Ronald Reagan and Franklin D. Roosevelt.

How? By understanding that politics is inescapably performative. Voters respond to signals. They respond to gestures of respect from politicians who are willing to say, in effect: We may not agree on everything, but I see you and understand what matters to you.

The newly energetic American left has largely rejected this approach, choosing instead to believe a comforting myth about swing voters being extinct and turnout being a cure-all. It’s a big mistake.

Before going further, I want to make clear that this is not a column urging Democrats to return to Clintonian centrism. I’m making a different case — that the left is hurting is own ability to win elections and enact sweeping change, by insisting on an orthodox version of progressivism.

To put it another way: Can you think of one way that Bernie Sanders is signaling respect to voters outside of his base?

He has taken a nearly maximalist liberal position on every major issue. It’s especially striking from him, because he has shown over his career that he grasps the importance of building a coalition.

Sanders once won over blue-collar Vermonters with help from a moderate position on guns. “We need a sensible debate about gun control which overcomes the cultural divide that exists in this country,” he said in 2015, “and I think I can play an important role in this.” He was also once an heir to organized labor’s skepticism of large-scale immigration. “At a time when the middle class is shrinking, the last thing we need is to bring over in a period of years, millions of people into this country who are prepared to lower wages for American workers,” he said in 2007.

Now, though, Sanders has evidently decided that progressives will no longer accept impurities — or even much tactical vagueness. He, along with Elizabeth Warren, has embraced policies that are popular on the left and nowhere else: a ban on fracking; the decriminalization of border crossings; the provision of federal health benefits to unauthorized immigrants; the elimination of private health insurance.

Article continues below

For many progressives, each of these issues has become a moral litmus test. Any restriction of immigration is considered a denial of human rights. Any compromise on guns or health care is an acceptance of preventable deaths.

And I understand the progressive arguments on these issues. But turning every compromise into an existential moral failing is not a smart way to practice politics. It comforts the persuaded while alienating the persuadable.

FDR and Reagan understood this, as did Abraham Lincoln and many great social reformers, including Frederick Douglass, Jane Addams, Martin Luther King Jr. and Cesar Chavez. Strong political movements can accept impurity on individual issues in the service of a larger goal: winning.

The impurities will still produce bitter complaints, of course. FDR and Reagan were both lambasted by their allies at times. But few of those allies abandoned them. Victory is an excellent balm.

Over the past few years, the progressive left has made impressive progress, elevating issues like the $15 minimum wage, expanded Medicare and free college. A central figure in the movement, Sanders, is now the favorite to win the Democratic nomination.

But progressives are still a very long way from achieving the changes they seek. Republicans control the Senate, and a conservative majority runs the Supreme Court. Trump has an excellent chance to win reelection and usher in a dark era for American progressivism.

Faced with the potential of either large gains or historic losses, progressives would be wise to stop believing only what they want to believe. Don’t cherry-pick polls to claim that most Americans actually favor a ban on private insurance. Don’t imagine that millions of heretofore silent progressive supporters will materialize on Election Day. In the 2018 midterms, Sanders-style candidates lost swing districts, while candidates demonstrating respect to swing voters won again and again.

Beating Trump in November will be even harder. And uncomfortable compromises will make it more likely.

For Sanders, that may mean walking back his position on fracking, which threatens his chances in must-win Pennsylvania. It could also mean repeating some of his earlier arguments about the need for border security and immigration restrictions. Many working-class voters, including people of color, agree with that.

Sanders is not an ideal Democratic nominee. But he does have some big strengths. One of them is the passionate support he inspires, which gives him an opportunity to reach out to new voters while holding on to his base.

David Leonhardt