As he prepares to join the hunt for a red November, former Tennessee Sen. Fred Thompson is walking into the line of fire.

Without raising a single campaign dollar or giving a single stump speech, Thompson threatens to knock one or more of the 2008 candidates out of the top tier -- and his 6-foot 6-inch frame will crowd out long-shot candidates who hope to emerge as the choice of social conservatives.

"I can't remember exactly the point I said, 'I'm going to do this,"' Thompson said of his planned presidential run in Thursday's edition of USA Today.

"But when I did, the thing that occurred to me: 'I'm going to tell people that I am thinking about it and see what kind of reaction I get to it."'

Thompson in the Spotlight

The move will also thrust into the spotlight a familiar face who nonetheless remains largely unknown as a political figure.

The conservative angst that has fed Thompson's ambitions has largely obscured questions about his stance on issues such as abortion, immigration and campaign finance reform -- not to mention his famously lax work ethic -- but that is set to change fast.

"At this point, he is a vessel into which many Republicans are pouring their hopes and dreams," said Whit Ayres, a Republican pollster who is not aligned with any of the 2008 candidates. "We know in general his values and his instincts, but that's not going to be enough to sustain a presidential campaign."

Independence Day

Thompson is moving toward announcing his candidacy in early July, according to two Republicans close to Thompson.

He plans to file paperwork June 4 with the Federal Election Commission that will allow him to begin raising money for a potential bid, and associates say he wants to start his campaign with a fundraising splash that will demonstrate his status as a viable candidate.

Over the past three decades, the 64-year-old Thompson has forged a unique career path that has left him shuttling between jobs in Hollywood and Washington.

He's perhaps known best known as District Attorney Arthur Branch on NBC's "Law & Order," but his career has also included roles in numerous blockbuster thrillers -- as well as a stint as a top counsel to the Senate Watergate Committee in the early 1970s.

It was in the Senate that Thompson developed most of his political reputation.

He won the race for the final two years of Al Gore's old Senate term in 1994, then won his own six-year term in 1996. He declined to run for re-election in 2002 after initially indicating that he would seek another term.

Thin Conservative Record

As a senator, he was known mostly for his work on investigative committees, and he developed a reputation as a less-than-stellar worker, a reputation that continues to dog him.

Wednesday the Democratic National Committee sent reporters a fact sheet purporting to detail the "major pieces of legislation" Thompson passed as a senator. The page was blank.

Thompson also left a voting record that has already become a subject of intense scrutiny in conservative circles.

He was one of the few Republicans to support the 2002 McCain-Feingold campaign finance reform law -- a measure that is loathed by many prominent conservatives -- and was one of only 10 GOP senators to have voted against one of the articles of impeachment filed against President Bill Clinton.

Though Thompson describes himself as "pro-life" and has called for Roe vs. Wade to be overturned, questions have been raised about whether he has always held that view.

While running for the Senate in 1994, he was referred to in several media reports as "pro-choice" and told an interviewer from a libertarian newsletter that abortion decisions "must be made by the woman. Government should treat its citizens as adults capable of making moral decisions on their own."

In addition, in a 1994 survey filled out for Project Vote Smart, Thompson checked a box saying, "Abortions should be legal in all circumstances as long as the procedure is completed within the first trimester of the pregnancy."

Thompson associates say that was an error made by a staff member. "Pro-life" groups judged Thompson to have a perfect record on abortion issues while in the Senate.

Though Thompson has railed against the immigration bill now before Congress, his longtime friend and former colleague, Sen. John McCain, R-Ariz., said that represents a position change for Thompson.

In April 2006, Thompson said on Fox News that he would support "a deal where [undocumented immigrants] can have some aspirations of citizenship" -- a position that some conservatives are likely to compare to "amnesty."

On Sunday, Republican presidential candidate Jim Gilmore said on ABC News' "This Week" that Thompson still has to prove that he has an established conservative record.

"The question is: Is there a solid, consistent record there of supporting conservative principles?" said Gilmore, a former governor of Virginia. "I don't think there necessarily is…He's got to come in and his record will have to be scrutinized, along with everybody else's."

Full Disclosure

Rep. Zach Wamp, R-Tenn., one of Thompson's biggest boosters in Congress, said Thompson is ready to answer questions about his record head on.

In a conference call with key potential fundraisers this week, Thompson answered numerous questions about his position on immigration, and explained his opposition to the current bill in detail, Wamp said.

"The more people get to know Fred Thompson, the more they'll like and respect him," he said.

At a meeting with House Republicans last month, Thompson even warned attendees that he was romantically involved with numerous women during his nearly two decades between marriages. (He married his second wife, Jeri, in 2002; the couple has two young children, in addition to Thompson's two grown children and five grandchildren.)

Republican Shake-Up

Polls have consistently shown Republican interest in additional presidential candidates, particularly one with a solid conservative record. Without any campaigning, recent polls have shown Thompson ranking third or fourth nationally in the GOP primary field.

Among the leading candidates, Thompson's candidacy would appear to pose the biggest threat to McCain and former Massachusetts Gov. Mitt Romney, both of whom are fashioning a campaign based largely on core conservative voters.

But polls have shown Thompson taking away some support from all the other candidates, including front-runner and former New York Mayor Rudolph Giuliani.

"You have a fairly significant number of activist folks who are not enthusiastic with what they see in the current field," said Michael Franc, vice president of government relations at the conservative Heritage Foundation. "People want to see good things, so they're only looking for a rationale to say, 'I want to go with this guy instead of that guy.'"

Even before getting into the race, Thompson has offered some hints about what his campaign might look like. He's become an active blogger, both at his own ABC News Radio site, and at popular conservative Web sites, where he has weighed in against the immigration bill in recent days.

He also got into a public spat with the liberal filmmaker Michael Moore, which culminated with Thompson filming a video clip in which he sucks on a cigar and suggests that Moore might belong in an "mental institution."

Thompson's biggest obstacle may be figuring out how to run a presidential campaign after several years outside of the political fray.

"The level of scrutiny ratchets up," Franc said. "The gotcha moments are going to start to arise, and he's not going to be allowed to do the sort of off-the-cuff things he has done so far."