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

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.

In U.S. Senate race, Coburn gains ground in August.

OKLAHOMA CITY -- Coming off of a competitive primary in late July, Tom Coburn (R) started the month of August almost even with his...