Rep. Mark Kirk (R) late Monday released a seven-week-old poll that showed him with a substantial lead over marketing consultant Dan Seals (D) heading into their November rematch.

Earlier this week, Kirk debuted on Roll Call’s list of 10 most vulnerable House incumbents, a calculation based on the Chicago North Shore district’s centrist leanings, a capable challenger and presumed outside involvement in the general election.

But the survey released by Kirk’s campaign suggests the outlook for Seals may not be as rosy as previously expected. In a ballot test, Kirk was well ahead of Seals, 50 percent to 29 percent. The remaining 21 percent of those interviewed were undecided.

The McLaughlin & Associates poll of 300 likely general election voters was conducted March 14-16 and had a 5.6-point margin of error.

The poll’s results also showed Kirk with a 61 percent favorable rating, with 21 percent of those surveyed saying they had a negative impression of the incumbent.

Kirk’s campaign also tested the increasing likelihood that popular home-state Sen. Barack Obama will sit atop the Nov. 4 ballot as the Democratic presidential nominee. Nearly one-third of the likely voters surveyed are self-described independents, according to Kirk’s campaign, whose votes undoubtedly would be up for grabs in an Obama matchup with Sen. John McCain (R-Ariz.).

According to the survey, those fence-sitting voters favored Kirk 2-1.

— Matthew Murray