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.