I call it pouring water on concrete. You make a splash, but nothing sinks in.

That’s what it has felt like lately arguing via tweet and email with supporters of President Dumpster Fire who insist there is “no evidence” he did anything to merit the investigations and talk of impeachment he now faces.

It is, of course, an astounding claim.

Donald Trump stands accused not simply by a contemporaneous memo from then-FBI Director James Comey and a series of rather damning reports, but also by his own words. Such as when he told Russia’s foreign minister and U.S. ambassador that he had just fired Comey, who was investigating whether Trump’s campaign colluded with the Russians last year when they meddled in the U.S. election.

“He was crazy, a real nut job,” said Trump. “I faced great pressure because of Russia. That’s taken off.”

And you wonder: How is that not obstruction of justice? If Bill Clinton lying about oral sex and Richard Nixon sacking a special prosecutor merited impeachment, how can anyone really believe there is “no evidence” Trump did wrong?

Anderson Cooper might feel my pain. You may have caught the CNN anchor last Friday watching in mounting disbelief as Trump surrogate Jeffrey Lord stumbled through one of his transparently disingenuous defenses of the president’s misbehavior. Finally, Cooper had had enough. “If he took a dump on his desk, you would defend it,” he said.

It was a coarse thing to say, yes. Cooper promptly apologized for it, as he should have. But one tends to empathize all the same. Because while the words might have been inappropriate, they were not incorrect.

Not that they will make a bit of difference. That’s the great frustration of political discourse in this era. Nothing seems to mean anything anymore. The idea of principled debate got run over by the Trump Train.

In its place, we have what Lord and an increasing number of like-minded sycophants represent: a brazen repudiation not simply of the facts, but of the fact that facts matter. We are trapped in a Groucho Marx routine: “Who are you going to believe, me, or your lying eyes?”

Consider that America was already a nation of ideological silos. If this is any indication, that’s about to get worse.

I say that reluctantly, as someone who has long prided himself on the ability to listen to and joust with those with whom I disagree. There’s always a chance you can learn something worthwhile from the other person. At a minimum, you’ll sharpen your own arguments.

But it has grown progressively more difficult to have those debates. One longs for an intellectually vibrant marketplace of ideas, but there is nothing intellectual or vibrant about what these days passes for conservatism. That once robust ideology has been shriveled by an intellectual dishonesty so profound that the same people who tirelessly investigated Barack Obama’s birth certificate and inveighed against his choice of mustard can look at the mountain of malfeasance rising from the White House and say with a shrug and all evident sincerity, “What evidence?”

How can you engage with that?

The good news is that facts remain factual, whether the somehow-still-employed Jeffrey Lord and people like him acknowledge that or not. Moreover, the facts in this case are already persuasive — and the investigations have miles yet to go.

Let that be enough. After all, one gets tired of wetting concrete. Better to save your water for places where there’s a chance something might actually grow.

Leonard Pitts is a columnist for The Miami Herald, 1 Herald Plaza, Miami, Fla., 33132. Readers may contact him via e-mail at lpitts@miamiherald.com.