Trump says if he runs in 2012, it would be as a Republican. If he does, the past positions he has taken would create almost insurmountable obstacles to winning the party's nomination.
Trump now says he's against abortion rights, but in his 2000 book, "The America We Deserve," Trump wrote, "I support a woman's right to choose."
In the same book, he also staked out positions on gun control that clash with GOP orthodoxy. "The Republicans walk the NRA line and refuse even limited restrictions," he wrote. "I generally oppose gun control, but I support the ban on assault weapons and I support a slightly longer waiting period to purchase a gun."
Trump also has switched party affiliations, at one time registering as a Republican, a Democrat and an independent, according to the New York Daily News. In 2009, he switched back to Republican.
"It's all perfectly legal, but the party base probably isn't going to like it. They'll naturally ask, 'Will he change again if elected?' " said Larry Sabato, professor of politics at the University of Virginia.
Trump's record of campaign donations also would be problematic. Although he has given generously to Republicans, he also has contributed more than $150,000 over the years to the Democratic Party and Democratic candidates, including such Republican bête noirs as Hillary Clinton, Rep. Charles Rangel (D-NY), Sens. John Kerry (D-Mass.) and Ted Kennedy (D-Mass.), campaign finance reports show.
As recently as January 2008, the records show, Trump made a $25,000 donation to the Democratic Senatorial Campaign Committee, the political operation that worked to keep the chamber in Democratic hands under Sen. Harry Reid (D-Nev.).
"In politics, only a fool automatically rules out anything. But it really is hard to imagine how Trump gets the GOP nomination. But that could simply be my failure of imagination," Sabato said.
The Reform Party's former national chairman Russ Verney met Trump a couple of times in 1999 as Trump pondered a Reform Party bid. "In fact, my wife and I were his guests Mar-a-Lago for a weekend," he recalled, referring to the Trump country club in Palm Beach, Fla.
Verney said he was "personally convinced that he (Trump) was sincere in his desire to run in 2000."
But, he added, "There was certainly no doubt in my mind that whatever exposure he got" helped Trump's business dealings. And what of Trump's musings this time around? "He is all about his brand," Verney said. "Whatever he does will turn out to his advantage."