Donald Trump has surged to the top of Republican 2012 polls after wholeheartedly embracing and vigorously touting in recent weeks the conspiracy theory that President Barack Obama was not born in the United States.

But the billionaire real estate mogul and reality TV star -- who insists he's serious about running for president -- has frequently changed his political leanings and policy positions on issues of interest to GOP voters. Although Trump has so far been unhindered by his flip-flops, presidential candidates ultimately have to answer for their past remarks.

Here are 10 past quotes that could sink Trump's hopes of capturing the Republican nomination.

1) "I probably identify more as Democrat."

--Interview with CNN's Wolf Blitzer, March 2004

2) "I've been around for a long time. And it just seems that the economy does better under the Democrats than the Republicans."

--Interview with CNN's Wolf Blitzer, March 2004

3) "Nancy — you're the best. Congrats. Donald."

--Handwritten note to Speaker Nancy Pelosi, January 2007

4) "Bush is probably the worst president in the history of the United States."

--Interview with CNN's Wolf Blitzer, March 2007

5) "I'm totally pro-choice."

--Interview with Fox News Sunday, October 1999

6) "I want to see the abortion issue removed from politics. I believe it is a personal decision that should be left to the women and their doctors."

--Remarks to reporters, December 1999

7) "I'm very liberal when it comes to health care. I believe in universal health care."

--Interview with CNN's Larry King, October 1999.

8) "The Canadian plan also helps Canadians live longer and healthier than Americans... We need, as a nation, to reexamine the single-payer plan."

--Writing in his book, The America We Deserve, January 2000

9) "By imposing a one-time 14.25 percent net-worth tax on the richest individuals and trusts, we can put America on sound financial footing for the next century."

--Writing in his book, The America We Deserve, January 2000

10) "I think he [Obama] has a chance to go down as a great president."

--Interview with NY1, November 2008