By Klaus Marre - 03/01/07 12:34 PM EST
"I am announcing that I will be a candidate for president of the United States," McCain said on "The Late Show with David Letterman."
But the senator noted that his statement was not the "formal" announcement, which he will make in April.
In 2000, the former Navy pilot ran for the White House but lost the Republican primary to President George W. Bush, who was favored by the GOP establishment. In that race, McCain earned accolades for his maverick style and "straight talk," and he endeared himself to independents and some Democrats.
But the senator, currently polling second behind former New York City Mayor Rudy Giuliani for the GOP nomination, has lost some of that support amid perceptions that he is moving to the right to appease the Republican base.
Most important, McCain has been one of the strongest supporters of Bush's plan to add more troops to Iraq. However, his views on campaign finance and immigration reform are not likely to sit well with many conservatives.