Chad Taylor, the Democratic candidate for Senate, sent a letter on Wednesday to the Kansas secretary of state saying that he was withdrawing from the race. He had been running against Pat Roberts, a three-term Republican incumbent. The race also has a viable independent candidate, Greg Orman, a businessman from Olathe. Mr. Taylor, the district attorney of Shawnee County, said he had consulted with his staff, supporters and Democratic Party leaders. He did not give a reason. Mr. Orman had positioned himself as Mr. Roberts’s strongest opponent, and his fund-raising was more robust than Mr. Taylor’s. Leroy Towns of the Roberts campaign accused Mr. Orman of engineering a “corrupt bargain” with the national Democratic Party. Mr. Roberts remains favored to win the race in Republican-leaning Kansas. Republicans have won every Senate contest in the state since 1932.