Donald Trump Preparing to Be 'President for All Americans,' Son Says

Donald Trump Jr. called it "overwhelming" to be in Washington, D.C., for his father's inauguration and said his dad, Donald Trump Sr., is now thinking about the "execution" of his inaugural address.

"He's been working on that for quite some time ... understanding the magnitude of that situation and really have that start off his entire presidency," Donald Trump Jr. told "GMA" by phone this morning from the president's guesthouse, where the Trump family spent the night. "He spent a lot of time with that, and now I think it's about execution."

Donald Trump Jr., one of five siblings, said that Thursday's festivities in Washington made his father's inauguration today as the 45th president of the United States seem real.

"After such a hard-fought battle, when you're in this thing for 18 months, really almost two years, when you're doing it every day, it takes a while to actually set in," he said. "Coming in yesterday, going to Arlington [National Cemetery], standing on the steps of the Lincoln Memorial, it really all set in for the family.

"It was very special."

Donald Trump Jr. said he watched his father evolve over the course of the nearly two-year presidential campaign as he met with Americans across the country.

"It's one thing to be out there and talking, but there's another thing when you see those Americans that he's talking about that haven't had a voice, those Americans who have watched their American dream shipped abroad, those Americans who have been through so many things," he said. "And you're meeting them, and you're seeing them face to face day in and day out for 18 months - you wouldn't be human if that didn't affect you."

He continued, "It drives home the gravity of the situation. It drives home the importance of the office and what he can accomplish there and for how many people he can accomplish it."

"After a campaign like this one, I think it's that he's going to be a president for all Americans," Donald Trump Jr. said. "It's not for a select few. It's not for some sort of special group. It's for every single American, each and every one of us."

Donald Trump Jr., who has five children with wife, Vanessa Trump, called it "really overwhelming" to see his father ascend to the presidency of the United States of America.

"And I'm not a person that tends to look at those things that way," he said. "It's truly special when you think of the significance and the history."

Speaking of the president's guesthouse, also known as Blair House, where Harry Truman spent his White House years and countless other dignitaries have stayed, Donald Trump Jr. said of the moment, "Thinking about it and looking at the walls and all the things that happened here and the people who stayed here and the major decisions that have been made here - and that's even before we get to the White House - it's like something I've never felt before."