Conservative groups smell blood in Arizona's 7th district.

Americans for Tax Reform (ATR), headed by Grover Norquist, has launched a TV ad hitting Rep. Raúl Grijalva (D-Ariz.) for calling for a boycott of the state. The 30-second ad ends by urging viewers to "vote no" on Grijalva.

Grijalva called for an economic boycott of Arizona after the state legislature passed its controversial law against illegal immigration. He's since backed away from those statements.

Still, two recent polls show Grijalva — who hasn't faced a tough challenge in his eight years in the House — within the margin of error against Republican Ruth McClung, a 28-year-old rocket scientist employed by a defense contractor.

McClung is backed by several prominent Republicans, including Sen. John McCain (Ariz.), former Massachusetts Gov. Mitt Romney and former Alaska Gov. Sarah Palin.

ATR, meanwhile, is spending $230,000 on the TV ad, which started airing on Wednesday, according to a spokesman for the group. To secure its support, McClung recently signed ATR's tax pledge, which states signatories will "oppose any net reduction or elimination of deductions and credits unless matched dollar for dollar by further reducing tax rates."

Democrats have used support for the pledge against other Republican candidates this cycle. The Democratic Congressional Campaign Committee has reserved TV airtime in the district starting on Oct. 26, according to a Republican strategist who tracks Democratic ad buys.