Politicians aren't usually prone to selfless acts of truth-telling. This doesn't mean they all lie all the time. But it does mean that they don't typically pronounce hard truths in isolation from considerations of political expediency.

So why did Hillary Clinton declare at a Manhattan fundraiser on Friday evening that half of Donald Trump's supporters are "irredeemable" — that they're so thoroughly "racist, sexist, homophobic, xenophobic, [and] Islamophobic" that they belong in a "basket of deplorables"?

A surprisingly large number of smart liberal pundits seem eager to defend and endorse her remarks — though some think she was right to back off on the false precision implied by "half" — and to lash out at the few mainstream analysts who have criticized the comments. Clinton told the truth, these liberals want us to know. That might make her comments a gaffe (defined as a statement that's politically damaging precisely because it's true). But it doesn't take away from their value in exposing and publicizing the alarming and dangerous character of Trump's support. The GOP nominee is a nasty man and so are many of those who plan to vote for him. That is the truth and it's a very good thing that the Democratic nominee is stating it loudly and clearly.

Now, it is indeed true that some indeterminate number of Trump supporters appear to be motivated by racism and other sordid sentiments. And it's also true that his campaign has emboldened extremists on the margins of the Republican Party. But these points have been made countless times over the past several months. The question is why Hillary Clinton chose to make that case in her own voice at a Manhattan fundraiser.

My hunch is that her motives were much less noble than Clinton's defenders seem to think, and that their own (understandable) disgust at the prospect of a Trump presidency is blinding them to what was really going on with her remarks.

When speaking in public, a politician can be motivated by a range of goals. She might be trying to persuade people to change their positions — to stop supporting another candidate and start supporting her. She might be trying to win a policy argument against those who hold opposing views. She might be trying to sway "swing" voters who are currently undecided among various options.

Clinton was obviously doing none of these things with her remarks.

Not a single Trump voter would hear Clinton's words and conclude, "You know what, I am deplorable! But I'm not irredeemable, and I'm going to prove it by dropping Trump and voting for Hillary Clinton instead!"

Neither was Clinton trying to win a policy argument.

Then there's the swing voter option. It's conceivable that some miniscule number of undecided voters might hear Clinton call out Trump's supporters as bigots, decide that she's right, and resolve not to associate with such people. But it wouldn't be nearly enough voters to explain putting such language in a speech.

It's far more likely that Clinton had a different intent. As with Mitt Romney's denigration four years ago of 47 percent of American voters, Clinton was speaking at a fundraiser, in this case one hosted by arch-liberal Barbra Streisand in a room packed with wealthy progressives. They were the intended audience of her comments — as well as others who might hear her words quoted afterwards and react similarly. Which is to say that Clinton was speaking to people who already consider Trump and his voters to be bigots and who would never consider voting for him.

We usually describe that kind of political speech as rallying the base. That's exactly what Clinton was doing.

There's nothing shameful about that. It's part of politics. A big part, especially in these days of sharp polarization and negative partisanship (in which many voters are motivated more by intense hostility to one of the parties than by support for either of them).

But analysts should never lose sight of the part their own words are playing in the political ecosystem. And the fact is that a Charles Blow column or a Greg Sargent tweet that doubles down on Hillary Clinton's anti-Trump-voter remarks is merely helping to whip up anti-Trump enthusiasm among people who already loathe Trump and everything he stands for.

It's Trump haters telling other Trump haters that it's the height of virtue to hate Trump and those who love him.

That's politics not as persuasion or policy argument but as masturbatory expressivism: one team intensifying its own political arousal to ensure that everyone does what he or she would have done anyway, though with even more enthusiasm than before.

In the case of Clinton's remarks, it's especially easy for liberal opinion journalists to lose sight of when they're at risk of serving as cheerleaders at a partisan pep rally. That's because some indeterminate number of Trump voters do hold blatantly illiberal and frankly deplorable views — and because journalists are often the target of alt-right abuse at Trump rallies and on social media. In that pressure-cooker context, with the political stakes enormously high, it can sometimes look like Hillary Clinton is less a politician trying to win an election than an extra-partisan champion of the unvarnished political and moral truth.

But of course the reality is more muddled than that. Clinton sees an electoral advantage in persuading Democrats that Trump is leading a dangerous movement of the irredeemably cretinous — and this despite the fact that on other occasions, like in her acceptance speech at the Democratic convention, Clinton has also pledged to be a "president for all Americans."

She comes closer to transcending politics with the latter sentiments.

The rise of right-wing populism is troubling to many, myself included. But as I've pointed out on more than one occasion, when the election is over the tens of millions who will have cast ballots for Trump will still be here, they will still have a vote, and they will still be our fellow citizens. Grievously insulting them simply isn't the wisest response.

Neither is cheering it on.