“In a Republican primary, if you’re in an ad supporting Barack Obama for president, that’s something that’s very, very unpopular with the base. Even if you’re in Illinois, that’s very unpopular,” explained Brian Nick, a GOP adman working for McKenna. “To be able to show that one of the front-runners endorsed Obama for president is a strong message to get out.”

Obama himself acknowledged the role he was playing in the GOP primary last week while appearing before House Republicans in Baltimore. In fielding a question from GOP Rep. Peter Roskam, a former colleague in the Illinois Legislature, Obama noted, “In the Republican primary, of course, they’re running ads of [Dillard] saying nice things about me. Poor guy.”

The Republican Senate primary, meanwhile, is emerging as an early ballot test of the tea party movement, with attorney Patrick Hughes aiming to cultivate conservative grass-roots support against Kirk, the establishment favorite.

Last week, Hughes began airing a TV spot blasting Kirk for his votes in favor of the bank bailouts and cap-and-trade legislation. “We need a conservative choice for U.S. Senate,” Hughes concludes in the ad.

So far, there’s little indication that Hughes’s candidacy has resonated broadly with the Republican electorate, with a Rasmussen Reports survey last week showing Kirk leading Hughes 53 percent to 18 percent.

Still, one Illinois Republican operative said Hughes’s campaign had the effect of moving Kirk to the right ahead of the general election campaign: In recent months, Kirk has sought the endorsement of former Alaska Gov. Sarah Palin and has appeared to backtrack on his support for cap-and-trade legislation.

“The question is who comes out of the primary more bruised — Kirk or Giannoulias,” said the operative.

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