(NewsNation) - Vice President Kamala Harris is working on her speech she will give at 4 p.m. ET today, a source familiar with her plans tells NewsNation.

"Thank you for believing in the promise of America ... We still have votes to count. We still have states that have not been called yet. We will continue overnight..." Harris campaign co-chair Cedric Richmond told dejected supporters gathered at Howard University on Tuesday night. Harris has not spoken publicly since polls closed.

Harris campaign manager Jen O'Malley Dillon sent out a letter to staff on Tuesday night, assuring them at the time that the current closeness of the race was "exactly what we prepared for."

In the email, O'Malley Dillon said staff have known all along that this is a "razor-thin race."

"While we continue to see data trickle in from the Sun Belt states, we have known all along that our clearest path to 270 electoral votes lies through the Blue Wall states," O'Malley Dillon wrote. "And we feel good about what we're seeing."

Harris called Trump on Wednesday to congratulate him on his victory. President Joe Biden also called Trump, the Associated Press reported.

Speaking to supporters at around 1:30 a.m. CT Wednesday, Trump said, "This was a movement like nobody's ever seen before.

"Frankly, this was, I believe, the greatest political movement of all time," Trump said. "There's never been anything like this in this country and maybe beyond, and now it's going to reach a new level of importance because we're going to help our country heal."

Trump's running mate and now Vice President-elect JD Vance, who also spoke, called the former president's win the greatest political comeback "in the history of the United States of America."

"He turned out to be a good choice," Trump said of Vance.