"The President will address the Americans who have been waiting for help from their leaders for too long, and let them know that help is on the way," Spicer told reporters.
"I think we are going to see a positive message and a vision that is carrying over from the campaign," said Rep. Doug Collins (R-GA), who expects a strong message about repealing the Obama health law.
"I think he's serious about his mission," said Rep. Robert Pittenger (R-NC) of the President. "He came here to be a change agent."
One unknown about tonight's address - will there be any notable protests of President Trump, whether from Democrats on the floor or people watching in the galleries?
There are Republicans who are worried about that, especially after recent dustups at Congressional town hall meetings.
"I am concerned that the environment that has been created about protests could be disruptive," said Rep. Mike Turner (R-OH).
"The decorum in this House should not stoop to that," said Rep. Ted Yoho (R-FL).
"I am concerned there is going to be disruption," said Rep. Barry Loudermilk (R-GA). "We did not do that to President Obama."
But before Loudermilk was elected to Congress, there was a moment like that in September 2009, when President Obama addressed Congress about his plans to reform health care, as Rep. Joe Wilson (R-SC), who is still in the House, shouted "You lie!" at Mr. Obama.
On Inauguration Day, a number of Democrats boycotted the Trump swearing-in and speech; it's not clear if some will do the same tonight.
"I don't know what I'm going to right at this moment," said Rep. John Lewis (D-GA) said on Monday night.
Each lawmaker gets a ticket for one guest - some Democrats are using that to make a variety of statements, bringing along people helped by the Obama health law and immigrant "Dreamers."
Mr. Trump has his own focus with guests - here is his list as provided by the White House:
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