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WASHINGTON (CNN) -- The 2008 race for the White House intensified Thursday as one of the big name Republican players, Sen. John McCain, threw himself into the fray.
The 70-year-old Arizona senator is the fourth Republican to say they will form an exploratory committee in the race for the GOP presidential nomination since the party took what President Bush called "a thumping" in the midterm elections.
Exploratory committees allow would-be candidates to raise campaign money without having to publicly disclose donations or expenditures. (Watch what led up to McCain's bid -- 1:55 )
McCain's name recognition can only be matched by former New York Mayor Rudy Giuliani, who filed papers with the Federal Election Commission to form a committee last week. The moderate conservative's performance in the wake of the September 11, 2001, attacks earned him praise and fame across the nation.
Rep. Duncan Hunter of California, outgoing chairman of the powerful House Armed Services Committee, was the first to form a committee.
On Wednesday, Tommy Thompson, a former Wisconsin governor who headed the Department of Health and Human Services in Bush's Cabinet during his first term, said he is considering a White House bid. An aide said Thompson is expected to create his exploratory committee early next year.
McCain posted a statement on his Web site Wednesday saying the move will "continue my conversation with the American people over the direction of the Republican Party and the future of our country."
"During the next couple of months, I will be talking with my family, friends and supporters about whether to officially announce a run for president," McCain said. "Prior to that decision, the formation of this committee is the first legal step in that process."
McCain is expected to file committee registration paperwork with the FEC on Thursday.
He will also spend the day delivering speeches to the Federalist Society, a group of conservative attorneys, and GOPAC, an education and training center for Republican candidates and activists across the country.
Registered Republicans surveyed in an October CNN poll about their 2008 presidential preferences put Giuliani and McCain at the top of the heap, well ahead of other possible contenders.
Giuliani was the choice of 29 percent; McCain, 27 percent.
McCain alienated religious conservatives in 2000
Serving his fourth term in the Senate, McCain is a former Navy pilot who was held for more than five years as a prisoner of war by the North Vietnamese after his jet was shot down in 1967.
He sought the GOP nomination in 2000, traveling around the country in a bus dubbed the "Straight Talk Express."
Although he won a few early primaries -- including a stunning upset in New Hampshire of George Bush, then governor of Texas -- his campaign faltered amid stiff resistance from religious conservatives, whom McCain often criticized.
To avoid a similar scenario, McCain has reached out to religious conservatives. In May, he gave a commencement address at Liberty University, founded by the Rev. Jerry Falwell.
Known for his generally conservative voting record, including opposing legalized abortion, McCain has not towed a typical Republican line.
He has supported campaign finance reform, for example, and he has called the ban on same-sex marriage "un-Republican."
The ban "usurps from the states a fundamental authority they have always possessed and imposes a federal remedy for a problem that most states do not believe confronts them," he said in July 2004.
McCain has also opposed the Bush administration's policies on the treatment and interrogation of terror detainees.
He angered conservative opponents of immigration by co-authoring a bill with Democratic Sen. Ted Kennedy of Massachusetts that would allow illegal immigrants to become guest workers. The idea is for illegal immigrants to work their way toward citizenship.
McCain, if elected, would be 72 when he takes office, making him the oldest person to ever win the White House. Ronald Reagan was 69 when he was elected in 1980.
Other Republicans who have been mentioned as 2008 possibilities are outgoing Govs. Mitt Romney of Massachusetts and George Pataki of New York, outgoing Senate Majority Leader Bill Frist of Tennessee, Sen. Sam Brownback of Kansas and former House Speaker Newt Gingrich of Georgia.
The 2008 election will be the first presidential contest in 56 years in which neither a sitting president nor vice president will be on the November ballot.
It will also be the first time in 80 years that neither the president nor vice president will be seeking his party's nomination.
Bush is constitutionally barred from seeking a third term, and Vice President Dick Cheney has said he will not run.
On the Democratic side, Gov. Tom Vilsack of Iowa has announced he will go directly to filing papers to run for his party's nomination, forgoing the usual exploratory committee.
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