Allen is the Senator who referred to an Indian representative of his opponent's campaign as a "macaca," a racial slur common in French North Africa, where his mother grew up. He also used to keep a noose hanging in his office, and several people who knew him in his college days have reported that he used to make common use of the epithet "nigger" (but not the word "epithet"), and two sources say that he once put the severed head of a deer in the mailbox of a black family.
Sherwood has admitted to having a lengthy (five-year) adulterous affair, and he settled a lawsuit which accused him of choking his mistress. His wife has referred to his affair as "a mistake."
Bush's press secretary Tony Snow addressed the president's support of Sherwood by observing that we are all sinners and deserve forgiveness. Forgiveness, perhaps. A seat in Congress, no.
UPDATE (October 20, 2006): Bush chose to campaign for these people of poor character during the same week that he has proclaimed "National Character Counts Week, 2006," a proclamation which begins:
America's strength is found in the spirit and character of our people. During National Character Counts Week, we renew our commitment to instilling values in our young people and to encouraging all Americans to remember the importance of good character.UPDATE (November 8, 2006): Don Sherwood lost, and it looks like George Allen will also lose.