Carson takes lead in U.S. Senate race as Coburn goes on the defense.

OKLAHOMA CITY -- The leader in the polls in the U.S. Senate race in Oklahoma has changed for a second time as Brad Carson (D) takes the lead in what is expected to be one of closest and most watched Senate races in the country.

SoonerPoll.com, a public opinion research firm in Oklahoma City, conducted the telephone poll of 412 statewide general election voters. The survey had a margin of error of 4.8%.

Since Labor Day, Tom Coburn (R) has found himself on the defense from comments he has made at several events, from calling state legislators 'crapheads', defining this race as one between 'good and evil', and questioning whether all members of the Cherokee Nation are Indians.

Just yesterday, a story surfaced about a former patient of Dr. Coburn who claims he sterilized her without her permission.

On behalf of Carson, the Democratic Senatorial Campaign Committee began television ads attacking Coburn for not voting to fund the Oklahoma City cross-town interstate project while in Congress. When asked recently by the media if he supported the project, Coburn replied, 'You bet.'

Carson's own TV ads have focused on his efforts for seniors, including his support for a prescription drug plan in Medicare. Meanwhile, Coburn's TV ads have focused on legislation he authored in Congress to reduce wasteful spending and his efforts to reduce the national debt.