'The World'

Retired Gen. Colin Powell, once considered a potential running mate for Sen. John McCain (R-Ariz.), now may endorse his opponent, Sen. Barack Obama (D-Ill.), according to Republican sources. But an air of mystery surrounds Powell's planned live appearance Sunday on NBC's "Meet the Press," and no one is sure what he will say.

Powell’s unassailable national security credentials could sway voters who are vacillating about whether Obama is ready to be commander in chief, and his endorsement of the Illinois senator would make a national security emphasis by McCain in the election's closing days extremely difficult.

Powell, 71, a professional soldier for 35 years, has advised the last three Republican presidents.

The general’s camp is being coy about what he might or might not say on Sunday. But some McCain advisers suspect, without being sure, that Powell will endorse Obama.

“It’s going to make a lot of news, and certainly be personally embarrassing for McCain," a McCain official said. "It comes at a time when we need momentum, and it would create momentum against us.”

Powell, a four-star Army general, was national security adviser to President Ronald Reagan; chairman of the Joint Chiefs of Staff during the 1991 Persian Gulf war, when George H.W. Bush was president; and President George W. Bush’s first secretary of State,

Powell has consulted with both Obama and McCain, and the general’s camp has indicated in the past that he would not endorse.

On “Meet the Press” in June 2007, Powell said: “I’ve met with Sen. Obama twice. I’ve been around this town a long time, and I know everybody who is running for office, and I make myself available to talk about foreign policy matters and military matters with whoever wishes to chat with me."

Asked by moderator Tim Russert if he would come back into government, Powell said: “I would not rule it out. I’m not at all interested in political life, if you mean elected political life. That is unchanged. But I always keep my, my eyes open and my ears open to requests for service.”

Asked about an endorsement, he said: “It’s too early.”

NBC’s ‘Andrea Mitchell broke the news of Powell’s surprise “Meet the Press” appearance on the “Today” show Friday.

“In what promises to be a dramatic moment Sunday, Colin Powell — a lion of the Republican establishment, whom McCain and Obama both have courted for months — will finally speak out on a variety of issues, appearing exclusively on ‘Meet the Press,’” Mitchell said. “Of course, years ago, he was talked about as the possible first … African-American nominee of a major party.”

Last week, Powell appeared as a character witness at Sen. Ted Stevens’ (R-Alaska) corruption trial, telling jurors that Stevens is someone he trusts completely. "As we say in the infantry, this is a guy you take on a long patrol," Powell said.