Missouri State Auditor Claire McCaskill (D) has moved ahead of Senator Jim Talent (R) in the latest Rasmussen Reports election survey to lead the incumbent 45% to 42% (see crosstabs). The candidates were tied at 42% in our survey last month.

While a 3-point lead for the challenger is well within the survey’s margin of sampling error, it is a concern for any incumbent to be so far below the 50% level of support at this point in the campaign. Four other Republican incumbents are in similar or even more difficult circumstances (Santorum in Pennsylvania, Burns in Montana, Chafee in Rhode Island, and DeWine in Ohio).

Both candidates register 83% support from voters in their own political party. Talent is tops among conservatives with 70% support while McCaskill leads with moderates (62%) and liberals (72%.)

While his overall numbers remain stagnant, Talent’s favorability rating has taken a five-point drop since June. Last month, 57% of voters reported a positive opinion of Talent; that number now stands at 52%. His unfavorable rating jumped from 37% to 42% during the same time period.

McCaskill’s overall favorable rating has dropped a point and now stands at 56%. However, the percentage of those surveyed who report having a very favorable opinion of the candidate has jumped from 19% to 24%.

The survey of 500 likely voters was taken on July 20, the same day that Talent’s new television ad, “Accomplishments,” launched. It will be interesting to note if the ad will give Talent any bounce in the next poll. In Washington, a new ad campaign turned around declining numbers for embattled incumbent Maria Cantwell (D)

Another issue in the race may be Talent’s vote against the Senate-passed legislation that would increase federal funding for embryonic stem cell research. McCaskill issued a statement via her campaign expressing her support for the measure and imploring the president to sign the legislation “for hope, for life.” A national survey found that 70% of Americans think such research has the potential to cure previously incurable diseases.

President Bush ultimately vetoed the legislation. In the current poll, 54% of Missouri voters disapprove of the president’s job performance with 43% reporting strong disapproval.

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