Is a State of the Union a speech or a campaign event? Either way, there'll be a fair bit of cheerleading going on.

That's because Americans who identify with the president's party almost always constitute a plurality or even majority of viewers, according to post-speech polling. In 26 of 27 State of the Union or similar joint addresses to Congress, more fellow party identifiers watched than people who identified with the other major party -- the one exception came in 1995, when Gallup found the same share of Democrats and Republicans took in President Bill Clinton's speech. In fact, a larger share of the audience often identifies as independent than with the opposition party, even though independents tend to be less politically engaged.

The degree to which Trump's speech will attract a more Republican-tilted audience could say something about how people are engaging -- or not engaging -- with politics at the start of Trump's second term. For Presidents George W. Bush and Barack Obama, their first joint addresses to Congress featured especially lopsided audiences made up of viewers who predominantly hailed from their party. Yet in Trump's first term, his initial audience was not as overwhelmingly Republican -- perhaps because people were especially curious to see what a Trump speech in a formal setting would look like.

-Geoffrey Skelley, 538

Several prominent Democrats announced that they would not be attending Trump's speech and instead will be offering their time to constituents.

Rep. Alexandria Ocasio-Cortez said earlier Tuesday that she would skip the speech in person, but would be posting about it on BlueSky and then doing an Instagram livestream after it was done.

Oregon Sen. Ron Wyden said he would be hosting a livestream on Facebook during the speech.

Just hours ahead of Trump's joint address to Congress, Congressional Black Caucus lawmakers held a fiery media briefing discussing their deep concerns for Black Americans during Trump's second term.

"This is theater tonight," former CBC Chairman Rep. Steven Horsford, a Democrat, told reporters. "He wants to distract us like he's done, so that he can do one thing, and that's to screw America. And Black America is at the top of his list."

Rep. Horsford and most CBC members said they would be attending Trump's joint address to Congress, but they decried his cuts to programs that they said directly impact Black families in America.

With American Federation of Government Employees members in attendance, the CBC described this as an "unprecedented moment" in America that is harmful to Black people and Black federal workers.

- ABC News' Arthur Jones II

A White House official told ABC News Senior Politics Correspondent Rachel Scott that Trump's remarks will focus on four parts: the president's record so far, the economy, border security and plans for "peace around the globe."

The president will push Congress to pass more border security funding for deportations and the border wall, the official said.

On foreign policy, the president is expected to touch on his efforts to help broker a peace deal between Ukraine and Russia. He is also expected to focus on his administration's efforts to bring home hostages amid the Israel-Hamas conflict.

Trump said “not long ago, and you can't even believe these numbers, one in 10,000 children had autism, one in 10,000 and now it's one in 36.”

He is correct about the current rate being one in 36, per the U.S. Centers for Disease Control and Prevention.

It’s not clear what year Trump was referencing for his “one in 10,000” statement, but in 2000 it was one in 150, according to the CDC.

There are reasonable explanations for why the rate is higher now than decades ago. The autism criteria shifted in 2013 when three diagnoses — autistic disorder; Asperger's syndrome; and pervasive developmental disorder, not otherwise specified — were merged into a singular autism spectrum disorder diagnosis, Evan H. Dart, University of South Florida associate professor in the school psychology program, previously told PolitiFact.

"This alone could explain large increases in medical diagnoses of autism since the 2000s, even more so compared to the 1980s," when autism first appeared in the Diagnostic and Statistical Manual of Mental Disorders, Dart said.

— Amy Sherman, PolitiFact