The Endorser. (Seth Wenig/AP)

The most terrifying thing of all in politics these days is when people reach across the aisle and say something nice.

No one has any idea how to respond.

There has to be a motive. Everyone is far, far too sophisticated to suspect that anyone might mean what he had to say.

It must be some sort of sinister Machiavellian scheme to gain power. No one has legitimate convictions.

Look what’s happened with Chris Christie’s thanks — and now, with Mayor Bloomberg’s endorsement.

Chris Christie has been touring the devastation of his state with President Obama, and he has been effusive in his praise of the president’s handling of the Hurricane Sandy situation.

Now New York Mayor Michael Bloomberg has endorsed Obama for a second term, citing climate change as his main reason for doing so, with nods to gay marriage and women’s rights.

Surely not! There must be some sinister motive.

As the floodwaters recede, the Sturm und Drang stays put, and its focus is anyone on the farther side of the aisle who dares say anything positive about the president.

Give credit where credit is due, and the commentariat reaches for its collective smelling salts. Everyone has spent the past three years assuring you that no action is undertaken for any motive other than political gain, and so the most convoluted explanations start crawling out of sewers.

Chris Christie is not sad that his state is devastated. He is deliberately scheming for 2016.

Michael Bloomberg is not genuinely concerned about climate change and doesn’t think that Sandy should be used to motivate action on this issue. He is grateful for a sneaky tax credit!

Of course, this devastating storm would strike the Northeast and its high-profile Republican or independent governors and mayors. Perhaps Sandy was in on it. It has slowed Romney’s momentum and filled his rallies with canned goods. Surely it’s been promised a job in the Obama administration.

Don’t we realize how ridiculous this sounds?

How polarized are we that we must constantly go ferreting out motives? Is it so impossible that occasionally someone might mean what he said? Perhaps I’m naive. But I’d rather be naive than so constantly paranoid.

Right now, no good deed goes unpunished. No kind remark, no frank acknowledgment of assistance, no joint appearance goes unscrutinized. No endorsement, however lukewarm, could be motivated by a sincere belief that one candidate addresses the issues better than the other.

I was hoping to be struck, in this crisis, by how we came together. Instead what struck me was how alarmed people were when we did.

Reach across the aisle? But across the aisle is where they keep the third rail. Say something nice, and everyone starts squinting at the television set to see if you are blinking in an unusual manner that might be a code. Say something nice, and doctors show up and start checking you for West Nile. Say something nice, and teams of experts start scanning your records for bribes and making certain no one has kidnapped your family.

After all, in these pre-election weeks, we aren’t Americans. We are Red America and Blue America. We will stop being so on Tuesday, but for something to come right now as our partisanship has been cranked up to fever pitch — and demand that people act bigger than that — is the Absolute Worst.

Yes, what Bloomberg is doing is different than what Christie did.

Christie thanked. Bloomberg endorsed.

The Bloomberg endorsement is already attracting attention for its focus on climate change and its effort to tie Sandy to humans’ impact on the environment. And while it’s difficult to point to any individual weather event and say, “This was the direct result of human action” — scientists have tried before, and this is not quite how things work, and any action we took now would only take effect decades down the road — the trends do bear examination.

But the immediate short-term response has been the same. Say one nice thing, and everyone starts looking for the gun to your back, the arm twist, the secret conspiracy.

“It’s the tax credit!” they are shouting. “It’s the fact that they both are fathers of two daughters and could not possibly understand the perspective of non-coastal elites!”

All this questioning of motives has been a national pastime for years. The idea that on the other side of the aisle are people trying their best, and that when they do something right, you should commend them? No. There be monsters.