When does The Club For Growth run ads in New Hampshire targeting an Arizona Senator? When he is likely Republican presidential candidate John McCain and the issue is the repeal of the estate tax.

In television ads that began airing Aug. 29 and are scheduled to run until the Senate votes on the matter, the conservative anti-tax organization is urging McCain to support full and permanent repeal of the so-called “death tax.”

The club is also targeting four Democratic Senators seen as vulnerable to pressure on the estate tax issue, and it has begun running ads in the special election to replace former Rep. Christopher Cox (R-Calif.). But it’s McCain for whom the group has reserved its biggest bull’s-eye.

“There’s one ad that is sharply critical, and that’s in New Hampshire on Sen. McCain,” Club President Pat Toomey said in an interview. “I think right about now he does care what the voters of New Hampshire are thinking — especially Republican voters.”

The ad targeting McCain accuses him of “wanting to keep” the estate tax.

In contrast, the ad pressuring Sens. Max Baucus (D-Mont.), Maria Cantwell (D-Wash.), Kent Conrad (D-N.D.) and Ron Wyden (D-Ore.) says each Democrat “can eliminate” it. Cantwell and Conrad could face tough re-election battles next year.

The difference in the ad scripts are subtle but not accidental, Toomey said, noting that McCain’s recent hints that he will vote for cloture on the matter are encouraging. Toomey declined to discuss the cost of the ad buy.

McCain’s office did not respond to requests for comment Friday.

Warren Henderson, chairman of the New Hampshire Republican State Committee, said repeal of the death tax is a hot-button issue for Granite State Republicans.

But because McCain is a known quantity in his state and the presidential primary is still three years away, the club’s ad is unlikely to have a lasting effect, Henderson said.

“Of everyone rumored to be candidate for president in 2008, Sen. McCain has a higher name ID then anyone else,” Henderson said. “To say that this issue, for this Senator, will have a lasting effect three years before the primary is probably kind of a stretch.”

Meanwhile, in the special election to replace Cox, who recently became chairman of the Securities and Exchange Commission, the club’s ads accuse former state Assemblywoman Marilyn Brewer (R) — a moderate who has been endorsed by McCain — of being a big spender without the courage to vote her conscience.

Toomey, whose group has endorsed state Sen. John Campbell (R) in that race, said the club is spending “well into the six figures” on television and radio ads that highlight what it says was Brewer’s failure to cast 362 votes while serving in the Assembly and her penchant for overspending.

“When she did show up,” the ad says, “she voted for a state budget that was so bloated, even [recalled Democratic Gov.] Gray Davis thought it spent too much money.”

Brewer campaign manager James Vaughn said the club manipulated the facts in the ad, particularly regarding her voting record.

The ad McCain filmed for Brewer, Vaughn said, is likely to have a bigger impact on this open-primary style election, as the district has seen a growth in moderate Republicans and Democrats with whom McCain polls well.

“The reaction we’ve had (to the club’s ad) has been positive,” Vaughn said. “It’s helped with fundraising — especially back in D.C.”

California Republican consultant Dan Schnur, who worked on McCain’s 2000 presidential campaign, disagreed with Vaughn’s description of the 48th district.

Not only is the district in Republican-leaning Orange County, but it is more conservative now than when Cox was first elected, Schnur said.

“In a low turnout special election, a third party ad buy will almost always make a difference,” he said. “But in an race like this where the Club For Growth matches up so well with the district, it could be even more potent.”