President Trump referred to a "Democrat agenda" in his State of the Union speech on Tuesday. He's said before that he prefers the term "Democrat Party" to Democratic Party, its official name.

But it's not grammatically correct — "Democrat" is a noun, "democratic" is an adjective — and it's also seen as a slight to Democrats.

NBC News national political correspondent Steve Kornacki, author of the book "The Red and the Blue: The 1990s and the Birth of Political Tribalism," says while the term doesn't have a specific date of origin, Republicans have used it as far back as the 1950s.

"[Sen. Joseph] McCarthy himself was known to use it. Other prominent Republicans of the period used it as well," Kornacki (@SteveKornacki) tells Here & Now's Jeremy Hobson. "The explanations that you heard back then were that they thought using the full, official name 'Democratic' suggested that they were kind of granting the premise that the Democrats were the party of the people. And then if you take that '-ic' suffix off of that, it changes the suggested meaning."

As Washington, D.C., enters a new period of divided government, something as small as dropping two letters off a party's official name could only serve to deepen partisan divisions, Kornacki says.

"Some Democrats kind of feel like it just sounds inelegant, it sounds rough, it sounds harsh, whatever word you want to put on it. So I think they're pushing back," he says. "They also just take it as disrespect — as a needless disrespect — as, 'Hey, this is the official name of our party. Call us by our name.' So I doubt they're going to turn around and embrace it too much."

Interview Highlights

On how use of "Democrat Party" has evolved over the years

"There were a couple of sort of eruptions along the way. There was one with Bob Dole when he was running for vice president back in 1976, he talked about 'Democrat wars' during a debate with Walter Mondale, his opponent. But really then it was in the 1990s, I think, when you had the rise of a new style of Republicanism in national politics that was kind of personified by Newt Gingrich. You had the kind of rise of a talk radio culture, Rush Limbaugh, and I think then it came back into prominence, and it's been there ever since."