Negative campaigning takes its toll on U.S. Senate race.

OKLAHOMA CITY - Ten days out and the race for Oklahoma's open U.S. Senate seat couldn't get any uglier. A poll by SoonerPoll.com, a public opinion firm in Oklahoma City, conducted Wednesday and Thursday showed Tom Coburn (R) with 38.0%, Brad Carson (D) with 36.8%, Independent Sheila Bilyeu with 5.8%, and 19.4% undecided.

The telephone poll, conducted for Fox25 News in Oklahoma City and KSWO-TV in Lawton, included 500 statewide likely general election voters, with a margin of error of 4.4%.

Last week, both candidates' numbers had risen over 40%, but this week both dropped, Carson taking the worst hit losing 6.5 points. Coburn, while losing 2.6 points, seems to be weathering the storm better than his Democratic opponent. Undecided voters climbed 5.4 points back to 19.4% where they have hovered since August due in large part to the overall negativity that has overtaken this race. Though Coburn has taken the lead for the first time since September, it is still within the margin of error.

The next week will prove pivotal for both candidates as conservative Democratic voters and moderate Republican voters, two groups that make up the largest percentage of undecided voters, begin to make their final decisions during the home stretch.

This week, two new ads were released once again accusing Tom Coburn of Medicaid fraud in the sterilization of an underage woman in the early 90's. The conservative Club for Growth released an animated ad showing a dancing Brad Carson and his liberal ties, and the Republican Senatorial Committee has shown ads insisting that a vote for Carson is a vote against President Bush.

Officials at both parties are also worried about turning out their voters on Election Day, due in large part to the heavy impact of negative campaigning.