In this fiercely competitive campaign, Democratic Missouri State Auditor Claire McCaskill now leads Republican Senator Jim Talent 45% to 42% (see crosstabs).

This is the tenth election poll showing the combatants separated by less than the margin of error. Rasmussen Reports has so far conducted eleven surveys of the contest.

Missouri remains one of six Toss-Up states in our Senate Balance of Power summary. The other Toss-Ups are Rhode Island, New Jersey, Montana, Ohio and Tennessee.

The incumbent led by a couple points in August--following a three-point lead by McCaskill in July—following a 42%-to-42% tie in June. It's been that way all year, a see-saw with a very short arc. Senator Talent thus remains one of the five or six most-vulnerable GOP incumbents in his chamber. (See our Senate Balance of Power summary.)

In early September, the campaigns began a flurry of negative campaign ads that pundits expect to continue unabated until Election Day, given how close the race is. The anti-Talent ads link the incumbent to ravenous "big oil"; the anti-McCaskill ads chastise her for liberal stances on social issues, immigration and national security.

McCaskill has not raised as much money as Talent but has been able to rely on strong financial backing from the Democratic Senatorial Campaign Committee.

The Democrat now has the edge with both unaffiliated voters and especially moderates. In August, the two were basically tied among unaffiliated voters, but McCaskill has enjoyed the same two-to-one advantage with moderates in both polls.

Her overall favorables are slightly higher than Senator Talent's. But Talent is viewed "very favorably" by more voters (27% versus the Democrat's 23%), as well as "very unfavorably" by more voters (21% versus 15%).

The economy is the most important issue to 25% of all voters, and to more unaffiliated voters and moderates (29%) than Republicans (15%). On national security, slightly more voters trust Republicans more. But on the economy, 51% trust the Democrats more, only 39% trust the Republicans more.

Crosstabs are available for Premium Members.