President Trump in Milwaukee on Friday. (Carlos Barria/Reuters)

With the first two nights of primary debates behind us, the Democratic presidential campaign season is now officially in full swing. The ostensible topics of contention are about what you’d expect from Democrats: health care, immigration, racial and sexual justice. But the subtext of all these arguments is a simpler, more visceral question: Which one of these candidates can most easily shove Donald Trump off the national stage?

At the moment, Sen. Kamala D. Harris (D-Calif.) is winning that silent primary. The kindest thing you can say about her policy positions is that they’re a pragmatic attempt to straddle the party’s moderate and progressive wings. The less charitable summation is that they’re an ineptly executed muddle; Harris keeps leaping frantically from pole to pole, rather than staking out some defensible middle ground.

But what does it matter that Harris isn’t much of a policy wonk? The important thing is that during the second night of the debates, she poleaxed former vice president Joe Biden with an unexpected, emotional question about his opposition to federal busing programs during the 1970s. Apparently, many Democrats are eager to see her do the same thing, only more so, when President Trump is on the stage.

It’s all been so exciting that almost no one has noticed the president steadily, quietly, turning into a more formidable opponent.

Over the past few months, Trump’s approval numbers have been slowly inching upward, and his disapproval numbers drifting gently south. They’re still abysmal, considering he’s presiding over the lowest unemployment rate in decades — but then, they were abysmal before he got elected. The gap between his approval and disapproval numbers is smaller than the gap was between his favorables and unfavorables in November 2016. And as my colleague Henry Olsen has pointed out, The Post’s latest poll shows him doing even better in key swing states such as Wisconsin and Ohio.

Is the public really that excited about the Trump administration’s new policy to improve treatment for people with end-stage kidney disease? They should be, because it’s great policy. But I suspect that there’s a simpler explanation: For the first time in several years, the media is starting to tune Trump out.

I’m not the first to observe that if the president wants better approval ratings, all he needs to do is shut up. Every time he stops tweeting, his numbers improve. Besides, the economy is good, and the public grows fond of presidents who preside over strong economies. Barring a recession, if Trump would just let the economic news speak for itself, he could probably sail to reelection.

Luckily for Democrats, Trump seems constitutionally incapable of learning from experience. Unluckily for the Democrats, their primaries are mimicking the effect of Trump holstering his Twitter finger. The media is now too busy analyzing the Democratic race to provide wall-to-wall coverage of Trump’s every tweet.

That won’t continue indefinitely; eventually, the Democrats will pick a candidate, and the spotlight will shift back toward Trump. But the higher his approval numbers go, the less beatable he looks. And the less beatable he looks, the more the Democratic Party’s choice of candidate and platform matter, because we’ve already seen that it is possible for Trump to beat a Democrat despite having high unfavorable ratings.

True-blue progressives will say we know all that, and argue that the party needs to move to the left precisely because they don’t expect 2020 to be a cakewalk. In these partisan days, there aren’t enough swing voters to matter; what matters is turning out the base, and you can’t do that on Republican Lite. If Hillary Clinton had turned out minority voters at the same rate as Barack Obama, she would have won.

That is, at best, debatable. What’s important is that if Trump’s approval ratings were better, the party wouldn’t even be having that debate. Activists always insist that their party needs to move toward its fringes to win. In normal years, the party ignores them and tries to swing toward the middle. And that seems like an especially fruitful strategy this year, because much of the middle is disgusted by Trump.

Instead, most of the candidates have been jostling to get on each other’s left flank. And now the #Resistance portion of the base seems to be flocking to Harris because she promises some cinematic fantasy of seeing Trump humiliated and vanquished on a debate stage.

It’s possible that this really is the way 2020 will be won. But it’s also worryingly possible that these strategies look feasible only because of an optical illusion — one that won’t resolve until the base has already damaged its party’s chances beyond repair.

Read more:

David Ignatius: Wake up, Democrats. Trump is on something of a roll.

Megan McArdle: Dear Democrats: I’ll vote for any of you. But please nominate someone who can actually win.

Paul Waldman: Why gender will define the 2020 election

Gary Abernathy: No one makes Trump as unsteady as Kamala Harris does