WASHINGTON — As a general rule, presidents do not refer to themselves as a “nationalist” given the freighted history of the word. But as President Trump tries to galvanize his conservative base to turn out in the midterm elections, he has adopted the label as a badge of honor.

At a rally in Houston on Monday night, he embraced the term as unabashedly as he ever has. “Really, we’re not supposed to use that word,” he told supporters in a nod to the usual political sensibilities that he relishes disrupting. “You know what I am? I’m a nationalist, O.K.? I’m a nationalist. Nationalist! Use that word! Use that word!”

Asked in the Oval Office on Tuesday why he used that word given its association with racist movements, Mr. Trump professed ignorance of its history but did not back off. “I never heard that theory about being a nationalist,” he said. “I’ve heard them all. But I’m somebody who loves our country.” Undaunted, he added: “I am a nationalist. It’s a word that hasn’t been used too much. Some people use it, but I’m very proud. I think it should be brought back.”

There is a reason other presidents generally do not use that word about themselves. Typically, the term “nationalist” is employed by the United States government to describe political figures and forces in other countries that sometimes represent a threat. When used domestically, it is a word often tainted with the whiff of extremism, not least because a variant of it, white nationalist, describes racist leaders and groups. American politicians traditionally stick with the safer term “patriot.”