When First Lady Jill Biden was asked in a CNN interview this week what she thinks of Nikki Haley’s call for “mandatory mental competency tests” for candidates older than 75, she didn’t hesitate. “That’s ridiculous,” she snapped. Would her husband, inquired the interviewer, consider taking such a test? “We would never even discuss something like that,” said Biden.

Haley made the proposal when she announced her presidential campaign. “In the America I see, the permanent politician will finally retire,” said the former South Carolina governor and ambassador to the United Nations. “We’ll have term limits for Congress. And mandatory mental competency tests for politicians over 75 years old.”

In the abstract, it makes perfect sense that people being considered for high-stress, high-stakes jobs should be able to demonstrate their mental competency. If US Air Force pilots, licensed doctors, and motor vehicle operators are required to meet appropriate standards of cognitive ability, why shouldn’t presidents and senators? In 2021, Senator Bill Cassidy, a Louisiana Republican who practiced medicine for 20 years before going into politics, came out in favor of cognition tests for elderly officials in all three branches of government. Cassidy wasn’t striking a political pose; he has focused on mental health issues as a lawmaker and was speaking, he said, “as a doctor.”

Haley, however, was striking a political pose. And as a political matter, mandatory mental competency tests are indeed, as Biden succinctly put it, “ridiculous.”

The only qualifications to be president are the ones listed in the Constitution: A candidate must be a native-born US citizen who is at least 35 years old and has lived in the country for a minimum of 14 years. There are no other prerequisites. Presidents are not obliged to own property, to have a college degree, to be a military veteran, or to have any political experience. Nor are they obliged to prove their cognitive fitness. In the absence of a constitutional amendment, a mandatory mental competency test is a nonstarter. The same, by the way, is true of congressional term limits: Until they are required by the Constitution, they cannot be imposed by statute.

And what if candidates could be forced to undergo a mental health evaluation? Would it make a difference?

Widespread concerns were raised about Donald Trump’s mental stability in 2016, and dozens of psychologists and psychiatrists penned an open letter in 2017 warning that he was “incapable of serving safely as president.” In the run-up to the 2020 election, 350 mental health professionals wrote that the evident deterioration in Trump’s mental health was becoming “ever more dangerous.”

Concern about Joe Biden’s mental acuity, meanwhile, has been no less prevalent. In opinion polls, respondents have consistently expressed doubts about the effects of Biden’s age on his intellectual abilities. During the last presidential campaign, the Trump campaign ran TV ads claiming that Biden lacked “the strength, the stamina and the mental fortitude to lead this country.” In January, an NBC News survey found that only 28 percent of respondents still think he has “the necessary mental and physical health to be president.”

Nevertheless, voters elected Trump to the White House in 2016, they elected Biden in 2020, and they may well reward one or the other with a second term in 2024. Americans don’t need to see the results of standardized tests to grasp that neither Trump, now 76, nor Biden, 80, is the sharpest knife in the drawer. Any such tests would in any case become grist for the political spin machine. Whatever the results, partisans would treat them as gospel truth if they supported their preferred candidate and as laughable pseudoscience if they didn’t.

For better or for worse, the framers of the Constitution and two centuries of American political tradition leave it up to voters to decide when a candidate is too old or incompetent to be elected to public office. To judge from recent presidential voting history — or from the way Congress is turning into a geriatric ward — most voters don’t mind being governed by the elderly and the decrepit.

Both Trump and Biden are well past their prime; I wouldn’t vote for either one of them. When Haley says that it’s time to move to a “new generation of leadership,” she’s right. But that will only happen if voters are persuaded to change their political behavior. Calling for a mandatory competency test? That’s merely a gimmick, not to be taken seriously.