Fred Thompson’s forthcoming announcement that he will seek the Republican nomination for President will push pollsters and conservative kingmakers to increase their scrutiny of the former Tennessee senator.

As an unofficial candidate Thompson dominated polls throughout the summer season of presidential campaigning. A September 5 Rasmussen poll found Thompson polling 23% among likely Republican primary voters. Thompson was only a point behind Republican front-runner Rudy Giuliani.

When asked if Thompson could be expected to receive a typical poll increase immediately after he announces his candidacy, president of Rasmussen Reports Scott Rasmussen said, “Thompson has been telling us he was going to announce for a long time, he’s been included in all the polls so I don’t know if we’re going to see as much as an impact from him as we did the others.”

“There are four people who are in double digits in the Republican race,” Rasmussen said. “All that Rudy Giuliani outpolls is the undecided category. So the undecideds are certainly going to be in play.”

As an unofficial candidate testing the waters for a national campaign, Thompson courted conservative-leaning groups, reportedly raised about $5 million and made a smattering of policy speeches.

Mike Franc, vice president of Government Relations at The Heritage Foundation said, “Thompson is entering the race with a proud conservative identity.”

“It’s not as if he is coming from center or left of center on the Republican spectrum. He’s yet another strong, articulate spokesman for conservative ideas and values and that can’t be bad for the movement,” said Franc.

Townhall.com spoke with a trio of advocacy groups that work to lower taxes about their perception of Thompson thus far.

President of Americans for Tax Reform Grover Norquist said he has asked repeatedly for Thompson to pledge not to raise taxes both as a U.S. senator and as a presidential candidate. Thompson has done neither. “We would like him to take the pledge,” Norquist said. “And unlike [John] McCain, he [Thompson] did not take it when he was a senator.”

Matt Kibbe, president of FreedomWorks said, “So far, it seems like Thompson is more willing to talk about real entitlement reforms based on personal accounts and ownership. Ownership is a good litmus test for whether a candidate is truly pro-growth and willing to stand up to the tax-and-redistribution Democrats who control congress.”

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.