The Arizona senator also launched a Web site — www.exploremccain.com — that allows supporters to donate and join his effort by donating money.
The four-term Arizona senator will deliver back-to-back speeches Thursday to organizations considered conservative cornerstones of the Republican Party — the Federalist Society and GOPAC. He will discuss the current and future state of the GOP.
McCain's move was expected; the senator discussed it Sunday on national television. He insists he will make no final decision about running for president until at least the last week in December.
Also Wednesday, former Wisconsin Gov. Tommy Thompson, who served as Health and Human Services Secretary in President Bush's first term, said he intends to form a committee to explore a possible run for the White House in 2008.
"I intend to do so after the first of the year," the Republican said in reference to establishing an exploratory committee.
McCain, a former Navy pilot who was a prisoner of war in Vietnam, ran against George W. Bush in the Republican primaries in 2000 and lost in a bitter race.
If McCain were to run again, he would turn 72 on Aug. 29, 2008, at the height of the campaign. Only President Reagan was older, 73 at the start of his second term.
And his views on Iraq might be a handicap, CBS News correspondent Gloria Borger reports. McCain's position is not only to continue the war, but to send in more troops. That's a very unpopular position in the country, as was illustrated by the midterm elections.
Over the past year, McCain has repeatedly demurred on questions about his political future and said he was focused entirely on helping Republicans get elected across the country.
He spent 2006 sowing goodwill within the GOP ranks, making 346 campaign appearances, raising $10.5 million for candidates and donating another nearly $1.5 million to their races. He directed most of his donations in the final month of the campaign to races in Iowa and New Hampshire.
In the meantime, his aides were busy building grass-roots organizations and lining up support in crucial states, including Iowa, New Hampshire and South Carolina, with local officials affiliating themselves with his political action committee — Straight Talk America.
At the national level, McCain beefed up his political operation by bringing on one-time Bush advisers to work alongside his own cadre of longtime loyalists.
Politically, he continued to build upon his reputation from 2000 as an independent in the party while also seeking to repair splinters with the conservative wing still angry over some of his positions.
He has been a forceful defender of Mr. Bush's Iraq policy, but also has put his own stamp on how the administration should handle the conflict. He has called for more troops to stabilize the country, placing him at odds with much of the country and to the right of many of his potential GOP rivals.
"Basically you're advocating the status quo here today which I think the American people in the last election said that is not an acceptable condition for the American people," McCain told Gen. John Abizaid at a congressional hearing Wednesday. "I regret deeply that you seem to think that the status quo and the rate of progress we're making is acceptable. I think most Americans do not."
Many fiscal and social conservatives alike remain skeptical about McCain, but the Republicans' losses in the last election actually could give him an opportunity to strengthen his standing with that crucial GOP base.
"The conservative folks are interested in leadership after last week," said Greg Mueller, a Republican strategist in Alexandria, Va. "He could use the liberal Democratic Congress as a foil in some ways to appease the conservatives and show leadership."
Thompson, who turns 65 on Sunday, spent nearly four decades in politics and government, including 14 years as governor. He resigned as HHS secretary in December 2004, shortly after Mr. Bush won a second term. His tenure at HHS was marked by anthrax attacks, a flu vaccine shortage and passage of the Medicare prescription law.
"We touched the third rail of politics and delivered on our promise to modernize Medicare with prescription drug coverage," Thompson said during a stop in Iowa.
Thompson argued that his background as a Midwest governor and HHS secretary would appeal to voters.
"The three big issues in 2008 are going to be health, energy independence and the war in Iraq," he said.
Thompson faces a daunting task in what's expected to be a crowded field of Republican presidential candidates. Former New York mayorin his bid.
Other potential candidates include Massachusetts Gov. Mitt Romney, Tennessee Sen. Bill Frist, Arkansas Gov. Mike Huckabee and New York Gov. George Pataki. California Rep. Duncan Hunter also has announced a presidential bid.
The Democratic field is shaping up early as well. As Borger reports, Hillary Clinton, D-N.Y., is the clear frontrunner. She has raised $21 million for Democratic candidates; she ran her own race very well, and won very handily.
Borger also puts Barack Obama, John Kerry, John Edwards, Joe Biden, Gen. Wesley Clark and possibly even former Vice President Al Gore on the potential Democratic candidate slate.