Rigell, with the backing of Virginia's Republican governor, is widely reported to be the front-runner in the race. In recent weeks, he's been criticized by his opponents for selling vehicles under last year's Cash for Clunkers program and donating $1,000 to Barack Obama's presidential primary campaign in 2008.
If he wins today, Rigell will join at least three other Republican dealer challengers in the November election: Mike Kelly in Pennsylvania; and Tom Ganley and Jim Renacci in Ohio.
A fifth dealer challenger, Bob Thomas in Indiana, lost his primary race in May. But he has a second chance after the winner of that race, incumbent U.S. Rep. Mark Souder, resigned after a sex scandal. Republicans in Indiana's 3rd District will determine their nominee at a June 12 caucus.