All 435 House seats are up every two years.
1/3 of the 100 Senate seats are up every two years--that's 33 seats every two years (34 seats every third two-year period).
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"People who say guns are bad are lucky enough never to have been in a situation where someone has kicked down your door and threatened the life of your son and your sixty-five-year-old mother."
-- Memphis, Tennessee resident Gina Cushon, quoted in Laura Ingraham's book "The Hillary Trap"