It seems all but certain that former senator and "Law & Order" TV star Fred Thompson will formally announce his campaign for president sometime after July 4.

Sources tell FOX News that the former Tennessee senator will wait until after Independence Day to announce in hopes of finding a more interested public, and the announcement could come as soon as July 5. Although plans have not yet been solidified.

And The Politico reported Wednesday that Thompson told a group of financial backers on Tuesday that he is going to run and had already raised millions of dollars. Thompson is encouraging more support as he readies his campaign in the crowded field of Republican candidates.

• Click here to read the report in The Politico.

The Politico also reports that a number of staffers to former Presidents Ronald Reagan and George H.W. Bush are expected to join Thompson's campaign.

Polls show that Republicans have not been satisfied with the current field of candidates. And even as an unofficial candidate, Thompson has pulled closely with former Massachusetts Gov. Mitt Romney, who is neck-and-neck with Arizona Sen. John McCain. For now, they are trailing former New York Mayor Rudy Giuliani.

Thompson is posturing himself as the more conservative alternative to would-be opponents Giuliani and McCain, and more steadfast than Romney, who is facing criticism for recently switching views on some conservative issues.

Thompson also is expected in early June to form a "testing the waters" committee, which is one type of precursor organization to an official campaign. While foregoing an exploratory committee, the filing still would allow Thompson to raise money in June in order to launch his candidacy in July.

Thompson does not expect to have the millions needed to compete aggressively in the Ames, Iowa, straw poll in August, but does hope to raise enough in June — including more than $1 million from a one-day telemarketing kick-off. Romney held a similar fundraiser in January pulling in $6 million.

FOX News' Carl Cameron contributed to this report.