It is simply the case that the candidates for public office never get better once they are elected to public office. At best, the candidate you see on the campaign trail is the mayor or governor or president you get. At worst, which is often the cases, the candidate you see on the campaign trail is actually the best version—with bigger promises and more manufactured charm—is actually the best version of the elected official who takes the position of power.

That’s politics. And voters need to be reminded of that fact as the election season hits its stride. No one should ever fall for the fantasy that a presidential candidate whose campaign-trail antics raise concerns will somehow turn out to be less concerning as president.

It never, ever, works that way.

Even the most exciting and encouraging contenders for the presidency tend to fall short of expectations. And candidates who are troublesome on the trail often turn out to be agonizingly awful once they sit down in the Oval Office.

This is a point that cannot be made frequently enough. And Michelle Obama, who knows a thing or two about campaigns and presidencies, is making it with perfect pitch this fall.

That the first lady is a powerful speaker and a powerfully effective campaigner has, by now, been well-established. What deserves more notice at this point in the campaign, however, is that she has emerged as the strikingly effective critic of Donald Trump.

When it comes to explaining why voters should be afraid, very afraid of the Republican nominee for president, no one does a better job than Michelle Obama.

Though she rarely mentions Trump by name at campaign stops on behalf of Hillary Clinton, the first lady’s references to Trump’s most obnoxious words and deeds put the billionaire’s candidacy in perspective. Precisely, and perfectly.

Michelle Obama can be blunt. She was getting a good deal of attention Wednesday for arguing that “we need an adult in the White House”—and for making it clear at a Pennsylvania campaign event that she does not think a 70-year-old man who makes crude comments about how women look or what they weigh meets the adult standard.

But the essential message of the first lady’s stump speech is subtler. She presents a thoughtful explanation of how to assess candidates for the presidency.

After arguing that “the presidency doesn’t change who you are, it reveals who you are,” she observed recently at Virginia’s George Mason University that “the same is true of a presidential campaign.” Then she nailed it:

So, if a candidate is erratic and threatening, if a candidate traffics in prejudice, fears, and lies on the trail, if a candidate has no clear plans to implement their goals, if they disrespect their fellow citizens, including folks who make extraordinary sacrifices for our country—let me tell you, that is who they are. That is the kind of president they will be. Trust me.

A candidate is not gonna suddenly change once they get into office. Just the opposite, in fact, because the minute that individual takes that oath, they are under the hottest, harshest light there is.

And there is no way to hide who they really are. And at that point it’s too late. They’re the leader of the world’s largest economy. The commander in chief of the most powerful military force on Earth. With every word they utter, they can start wars, crash markets, change the course of this planet

So who in this election is truly ready for this job?

That’s a simple, direct statement—followed by a simple, direct question.

Yet, it speaks a truth that ought to be writ large across the 2016 campaign. As an Atlanta Journal Constitution headline wisely observed earlier this month: “There is no Trump but this Trump.”

Too much energy has been wasted on efforts to detect a different Trump, a better Trump.

But he never shows up. Not at his convention. Not at his campaign stops. Not in his media interviews. Not at Monday night’s first debate with Hillary Clinton. Even when the billionaire nominee is on “best behavior,” the cruel and unusual “Donald” invariably erupts.

There is no better Trump waiting to emerge at a critical point in the campaign. There is no nicer, more humane and responsible Trump waiting to take the oath of office. This is the Trump we’ve got. And, were he to be elected president, this is the Trump America would be stuck with.

Don’t say that Michelle Obama didn’t warn you.