It’s been a rough week for Democrats. President Donald Trump is preening over his acquittal, his poll numbers and the economy, while the Democratic nomination race looks like a divided mess. Many Democratic voters are anxious that they have no great candidates, only those guaranteed to alienate one half of the party or the other.

Moderates worry that Bernie Sanders and Elizabeth Warren aren’t just wrong on big issues, but too left wing to get elected. Progressives worry that Pete Buttigieg, Joe Biden, Amy Klobuchar and Michael Bloomberg are uninspiring centrists who resemble recent presidential losers and wouldn’t solve America’s problems even if they won.

My message to panicking Democrats is: Take a deep breath, and don’t make your job harder. Neither side of the party can ensure that its preferred candidate will win the nomination. But both can help avoid the outcome they fear most — Trump’s reelection.

The current moment, when everybody is wearing a veil of ignorance about the nomination, is a good time for Democrats to ask themselves a question: If the primaries don’t turn out as you hope, will you still do everything in your power to deny Trump a second term?

Or will you instead exaggerate your differences with the nominee — say, complain about Sanders or Warren as a Trump-style radical; or buy into the caricature of Buttigieg as a corporate tool; or retweet, with outrage added, the least enlightened things Biden or Bloomberg has ever said?

Yes, the candidates have their differences. But they have much bigger similarities. If elected, every single Democratic presidential candidate would act to slow climate change, raise taxes on the rich, reduce gun deaths, expand voting rights, lower health care and education costs, protect abortion access, enforce civil-rights laws, appoint progressive judges, rebuild overseas alliances and stop treating the Justice Department as a personal enforcer. The moderates are running to the left of Barack Obama, and the progressives would be constrained by Congress.

The alternative, of course, is truly radical. Many Democrats know all this, yet they still get so caught up in the passions of the primary campaign that they risk helping Trump.

Whether progressives and moderates can find common ground is likely to be a defining political question not just of 2020 but of this decade. As E.J. Dionne asks in the first sentence of “Code Red,” his new book, “Will progressives and moderates feud while America burns?”

Dionne, a Brookings Institution senior fellow and Washington Post columnist, tells a story about American politics that I find clarifying. In the past, thorny policy debates typically took place between the two parties. Examples include the best way to expand health insurance (through the private sector or government), control pollution (through taxes or regulations) and reduce the deficit (through spending cuts or tax increases).

Today the Republican Party has become so radicalized that it opposes almost any government action to solve problems. Its domestic agenda consists largely of cutting taxes for the rich and freeing companies from oversight. The substantive part of many policy debates now happens within the Democratic Party — which means that tensions are only natural.

And yet progressives and moderate Democrats still agree on far more than they disagree. Each side would be more effective if it were open to learning from the other, Dionne writes, rather than lapsing into “an unseemly moralism that feeds political superiority complexes.”

Progressives are right that over the past half century, Democratic moderates have often allowed conservatives to dictate the terms of political conversation, on economic growth, criminal justice, family values and more. I’d add that moderates have also spent too much time designing technocratically elegant policies (like tax credits) rather than creating easily understandable, popular programs.

Moderates, for their part, are right that every great progressive victory in American history — abolition, women’s suffrage, the income tax, labor rights, Social Security, civil rights, Medicare, marriage equality and more — has required compromise in the service of persuading allies who disagree with progressives on other issues. It’s not enough to state your case purely and wait for a silent progressive majority to emerge as never before.

In the long run, each side is likely to accomplish much more if it can recognize that the other isn’t the enemy. In the short run, obviously, there is an inescapable dilemma: The party can nominate only one person.

Before that choice is made — while both sides are fighting hard for their preferred nominees, as they should — they should pause to reflect on the strengths of the other side. For progressives, that means recognizing that moderate congressional candidates really did fare better in swing districts in 2018. It also means celebrating (quietly, for now, I realize) the progressivism of, say, Buttigieg’s agenda.

For moderates, it means acknowledging that Sanders’ pugnacious authenticity appeals to some swing voters more than wonkish centrism does. And it means pushing back against the false notion that Sanders and Warren are somehow un-American. A Sanders or Warren presidency would have more in common with Dwight Eisenhower’s presidency than a second Trump term would have with either of them.

The 2020 campaign still has a long way to go. Democrats should remember which parts of it they can’t control and which they can.

David Leonhardt

David Leonhardt is an Op-Ed columnist for The New York Times.