Pat Toomey, president of Club for Growth said, “Fred Thompson’s formal entry into the race marks the beginning of phase two. The big story of phase one was the collapse of McCain,” Toomey said. “In phase two, it’s largely about whether or not Thompson can meet the very high expectations that have been set for him.” The Club for Growth will distribute a “white paper” on Thompson’s record on taxes shortly after his Thursday announcement.

Earlier this year, media reports surfaced that said Thompson had lobbied for an abortion rights group after he left the Senate that caused an intense debate in the blogosphere over Thompson’s conservative bona fides.

Editor of Redstate.com Erick Erickson applauded Thompson’s record on social issues. “If we assume that McCain is done, that leaves a pro-choice candidate [Giuliani] and a pro-life by convenience candidate [Mitt Romney] running for the nomination,” Erickson wrote in an email. “Of Giuliani, Romney, and Fred, Fred is the only one with a 100% pro-life record in elective office.”

The former Tennessee senator will officially declare his candidacy on September 6, a day after the September 5 Fox News Republican presidential debate in New Hampshire.

Instead of appearing alongside the declared candidates, Thompson has purchased a television advertisement to preview his next-day announcement that will air during the debate. In the ad Thompson says: “On the next President’s watch our country will make decisions that will affect our lives and our families far into the future. We can’t allow ourselves to become a weaker, less prosperous and more divided nation. Today, as before, the fate of millions across the world depends upon the unity and resolve of the American people. I talk about this tomorrow on Fred08.com. I invite you to take a look and join us.”

Thompson will also make an appearance on NBC’s “Tonight Show” with Jay Leno late Wednesday evening, after the Fox News debate has finished.