President Trump said Sunday that he was "close to making a decision" about who he would nominate to replace retiring Supreme Court Justice Anthony Kennedy a little more than 24 hours before he was scheduled to announce his choice in a primetime address Monday.

"I'm very close to making a final decision. And I believe this person will do a great job," Trump told reports as he left for Washington from a weekend at his New Jersey golf club.

When asked how many people were being considered, the president said: "Let's say it's the four people ... they're excellent, every one. You can't go wrong." Trump added that he would make his final decision "tonight or tomorrow sometime by 12 o'clock and we're all gonna be meeting at nine o'clock."

Later Sunday, Trump tweeted that he was "[l]ooking forward to announcing my final decision on the United States Supreme Court Justice at 9:00pmE tomorrow night at the @WhiteHouse. An exceptional person will be chosen!"

The Trump administration has been preparing information materials on four potential nominees: appeals court judges Brett Kavanaugh, Raymond Kethledge, Amy Coney Barrett, and Thomas Hardiman.

Sources who talked to Trump Sunday morning tell Fox News that the president's top two choices are Kavanaugh and Hardiman, though a GOP source said late Sunday that Barrett still has a good chance of being the pick.

Hardiman was the runner-up when Trump nominated Neil Gorsuch to replace the late Justice Antonin Scalia last year. He also has a personal connection to the president, having served with Trump's sister on the 3rd U.S. Circuit Court of Appeals in Philadelphia.

Each possible choice must be balanced against political realities -- with Republicans holding a razor-thin majority in the Senate and Democratic leaders imploring their colleagues to stand firm against any Trump nomination.

Some conservatives have expressed concerns about Kavanaugh — a longtime judge and former clerk for Kennedy — questioning his commitment to social issues like abortion and noting his time serving under President George W. Bush as evidence he is a more establishment choice. But his supporters cite his experience and wide range of legal opinions. Barrett has excited social conservatives since she was questioned about her Roman Catholic faith in her nomination hearings last year, but her brief time on the bench has raised questions.

Sources tell Fox News that Sen. Susan Collins, R-Maine, has expressed concerns about Barrett to the White House. The Trump administration believes she would ultimately vote to confirm Barrett, but she does not want to be boxed in. Trump also has to decide if he wants a nominee that will propel abortion to the forefront of the confirmation battle. Collins has previously said a nominee who opposes Roe v. Wade, the 1973 case that legalized abortion nationwide, would be "unacceptable."

Top Republican senators said Sunday that they were confident that any of the four finalists could get confirmed by their colleagues.

Sen. Lindsey Graham, R-S.C., told "Fox News Sunday" that Democrats from states won by Trump in 2016 "are going to have a very hard decision."

"There's nobody that President Trump could nominate from a conservative bent that will get many Democratic votes," Graham said, "but this is a nightmare for red states Democrats to oppose a highly qualified nominee, and all four of these people are highly qualified, been on the court, know what they’re doing, mainstream judges ... and I hope every Republican will rally behind these picks because they’re outstanding."

Three such Democrats -- Joe Manchin of West Virginia, Heidi Heitkamp of North Dakota and Joe Donnelly of Indiana, voted to confirm Gorsuch along with 51 Republicans last year.

"They're good judges," Sen. Roy Blunt, R-Mo., told NBC's "Meet The Press. "I think they'd be fine justices of the Supreme Court. I do think the president has to think about who is the easiest to get confirmed here. And I expect we will do that on sort of a normal timetable, a couple of months."

Trump's outside judicial adviser Leonard Leo, currently on leave from the Federalist Society, said on ABC's "This Week" on Sunday that this kind of jockeying is standard, noting that "every potential nominee before announcement gets concerns expressed about them by people who might ultimately support them."

Leo said: "Brett Kavanaugh and Amy Barrett have a lot of name recognition among supporters of the president, and I think that ultimately when people like them are nominated, you'll see a lot of folks line up."

Of the other two, he added: "Ray Kethledge and Tom Hardiman, they're a little bit less known by conservatives. And their records are a little bit lighter. So, it might take some time."

Fox News' John Roberts and The Associated Press contributed to this report.