But maybe Democrats do not want to be competitive in the Bible Belt. No retreat on feticide, no compromise with Gilead! Fair enough. Then presumably they should want to make up ground with more secular voters somewhere else — among all the lapsed Catholics and former Mainline Protestants scattered around the Midwest, for instance.

Some of these voters pulled the lever not once but twice for Barack Obama, and then voted Trump in part because of anxieties about recent immigration. So are the Democrats trying to dispel the impression that their party favors open borders? No, quite the opposite: As Vox’s Dara Lind pointed out this week, in the Trump era, no less than the Obama era, the Democrats are rejecting enforcement proposals many of them would have championed a decade ago — again, not coincidentally, the last period when they had control of Congress. Wooing immigration-wary Midwestern voters, like doing outreach to pro-life moderates in Alabama, is apparently not worth the compromises required.

Now I am a cultural conservative, so naturally issues like abortion and immigration are the places where I would like the Democratic Party to move closer to the center. One could argue instead that Democrats should stick with progressive orthodoxy on social issues and choose Bill-Clintonian economics over single-payer flirtations, to expand their recent gains among the culturally libertarian and fiscally conservative.

But the point is that a party claiming to be standing alone against an existential threat to the republic should be willing to move somewhat, to compromise somehow, to bring a few of the voters who have lifted the G.O.P. to its largely undeserved political successes into the Democratic fold.

Instead, the Democrats are still relying on arc-of-history beliefs and long-term demographic trends. But those trends do them no political good if they move left faster than does a leftward-moving country. In 2004 they had an agenda well-suited to the American electorate of 2016; having moved leftward since, they now have an agenda well-suited to the American electorate of 2030.

If current trends continue the Republicans will nominate a ticket of Roy Moore and Tomi Lahren in 2024 — and the Democrats, secure in their historical destiny, will counter by replacing their platform with a loving commentary on John Lennon’s “Imagine.”

As much as the country needs a conservatism with some idea of what it’s doing, some theory of the common good, it needs a liberalism that stops marinating in its own self-righteousness long enough to compete effectively for rural, Southern and Midwestern votes.

But you can’t always get what you need.