By Cokie Roberts and Steven V. Roberts

Joe Biden is aiming his campaign pitch directly at the sensible center of American politics.

“Compromise itself is not a dirty word,” he asserted during his announcement speech in Philadelphia. “Consensus is not a weakness. It’s how our founders down the road thought we would govern.”

As a governing strategy, Biden is clearly correct. Particularly in an era of divided partisan power, consensus-building is the only possible way to advance progressive goals. On the issues that liberals care deeply about — from paying for college to expanding health care — no compromise means no action. Purity equals paralysis.

As a political strategy, Biden is also right. The clamorous ideologues in the loud left wing of the party get a lot of attention on social media, spreading the myth that Democratic successes in 2018 were based on a lurch away from moderation. That’s totally wrong: Their House majority was secured by “right-down-the-middle, mainstream, hold-the-center victories,” as Speaker Nancy Pelosi puts it.

A winning strategy next year has to learn from that experience. The path to the White House does not run through the campuses of Berkeley and Cambridge; it runs through the suburbs of Pittsburgh and Detroit.

“The left makes a lot of noise. They get a lot of press,” Elaine Kamarck, a shrewd Democratic strategist, told The Washington Post. “When people vote in primaries and they know the general election is competitive, there is plenty of evidence to show they make sophisticated judgments about who can win.”

So far, the polls back up her analysis — and Biden’s appeal. An average of national surveys gives the former vice president a 20-point lead among Democratic voters over his closest rival, Sen. Bernie Sanders. A recent Gallup poll reports that 54 percent of Democrats want their party to move closer to the center, with 41 percent advocating a shift to the left. And in a Monmouth survey, 56 percent of potential Democratic voters placed top priority on picking a candidate who can defeat President Donald Trump; only 33 percent preferred a nominee who aligns with them on issues.

This is all good news for Biden, but he is hardly an ideal candidate. He’s run for president twice before and flamed out both times. He has a well-earned reputation for damaging mistakes and missteps, and his handlers cannot shield him from media questions indefinitely. He’d be almost 78 on Election Day, 31 years older than the average age of the last four non-incumbent Democrats to win a presidential election (Kennedy, Carter, Clinton and Obama).

And like Hillary Clinton in 2016, Biden struggles to portray himself as a change agent. In fact, the change he represents is largely backward-looking: a return to an earlier era, not an advance into a new one.

“I’m going to say something outrageous: I know how to make government work,” he said in Philadelphia. “Not because I’ve talked or tweeted about it, but because I’ve done it. I’ve worked across the aisle to reach consensus.”

Liberal critics point out that Republicans mounted a ferocious opposition to President Barack Obama for eight years, and they deride compromise and consensus as impossibly archaic ideals.

“Washington is in post-deal-making mode,” said Jeff Hauser of the left-leaning Revolving Door Project to Politico. “The last tiny remaining vestiges of that world ended with the rise of social media and Trump, and skill at ‘grand bargains’ is about as relevant to modern politics as skill with a physical Rolodex.”

Biden was strongly criticized from the left, for example, when a campaign aide said he would follow a “middle ground” on climate change. “There is no ‘middle ground’ when it comes to climate policy,” thundered Sanders. But Biden is betting that Sanders and his acolytes are wrong. Climate change is a highly complex issue involving powerful economic, political and cultural forces. Any progress toward mitigating global warming has to reflect a “middle ground” consensus that recognizes and reconciles those forces.

The same is true for thorny problems like health care, immigration and countless others.

At a campaign stop in New Hampshire, Biden predicted that bipartisanship would become easier again in a post-Trump world. If Washington cannot change the current climate of hyper-partisanship, he added, “We’re in trouble. This nation cannot function without generating consensus. It can’t do it.”

The next president will have a hard time making “compromise” a noble word again in American politics. That might not be Biden, but he or she must try. And yes, we are in trouble if that effort fails.

Steve and Cokie Roberts can be contacted at stevecokie@gmail.com.