Jabs between President Trump and Rep. Maxine Waters (D-Calif.) aren’t new. But Trump's latest comments are a reminder of how often he will go out of his way to personally attack the black women who challenge him.

The liberal lawmaker has been one of the most vocal critics in Congress of the president’s policies and made comments deeming him unfit for office before he entered the White House.

But while campaigning for Rick Saccone, a Pennsylvania state legislator running for Congress, the president directed his attention toward the West Coast politician.

“Did you ever see her? Did you ever see her? 'We will impeach him. We will impeach the president,' " Trump told the crowd.

" 'It doesn't matter, we will impeach him.' She's a low-IQ individual,” he added. “You can't help it.”

Waters told the crowd at the California Democratic Convention last month that “it is time to get ready for impeachment,” based on the latest updates from special counsel Robert S. Mueller III’s investigation of the relationship between the Trump campaign and Russia.

“I cannot wait, and I'm counting on special counsel Mueller to connect the dots,” Waters said. “I believe he's getting closer to discovering that Americans were and are involved in collusion with the Russians.”

Although Waters shared why she thinks Trump will be impeached, the president did not explain why he thinks Waters has a low IQ.

What has been explained before is the role IQ tests have played in discriminating against women and people of color.

In 1905, French psychologist Alfred Binet developed the first IQ test intended to identify children with learning disabilities, but many Americans soon began to use the exam to justify systemic discrimination.

Author Dana Goldstein wrote in Slate:

“IQ quickly enraptured American researchers, who were eager to find a scientific justification for the nation’s racial hierarchy. Carl Brigham, who later developed the SAT, studied the IQ scores of over 1 million World War I recruits. Brigham and colleagues claimed that the scores showed native-born whites as the most intelligent group, followed by immigrant Italians and Jews, and then black Americans. But IQ exams never tested innate smarts. … It was unsurprising that poor people, with less access to good schools and less familiarity with middle-class white American culture, scored lower. Nevertheless, low IQ scores were frequently used as a justification for sterilizing and incarcerating people.”

Given this history combined with Trump’s past comments about black people, it’s no surprise that some, including Waters, interpreted his comments as racist.

And that was exactly Waters’s response to Trump attacking her IQ a week earlier at the annual Gridiron Club annual dinner. Shortly after that, she told MSNBC’s Joy Reid: “I certainly expected him to come out with some racist remarks about me. So he did exactly what I expected him do. And, by the way, I’m told he wasn’t funny at all.”

Perhaps Waters expected Trump’s remarks — and Treasury Secretary Steven Mnuchin’s excusing of them — because of his history of challenging black women who have criticized him.

When considering his past comments about Oprah Winfrey, ESPN journalist Jemele Hill, Rep. Frederica S. Wilson (D-Fla.), former national security adviser Susan E. Rice, former Democratic National Committee chairman Donna Brazile or Waters, some think Trump's attacks against black women reek of sexism and racism in ways that his other attacks do not.

“Whether it’s a knowing choice from the president or it stems from his utter lack of restraint, the attacks reflect his twin contempt for women and nonwhites,” Slate's Jamelle Bouie previously wrote. “Trump pushes back against most criticism, but when it comes from a prominent black woman, the response is more aggressive, more interested in making a spectacle — and an example.”

Mnuchin played down the dismissal of Waters on Sunday as “campaign rally issues.”

“I’ve been with the president and at campaigns. You know, he likes to put names on people,” he said Sunday on NBC’s “Meet the Press.” “He did that through the entire presidential election, including all of the Republicans that he beat. … These are campaign rally issues.”

Attacking political opponents might win Trump points from those who already are so invested in his presidency that they attend his campaign rallies. But considering how poorly Trump is doing among women and black voters, bringing into question the intelligence of leaders who represent these communities because of their support for an investigation seeking to get to the bottom of Russia’s involvement in an American campaign is not the best way to get them to board the Trump train.