Much of the Hudson River Valley, in all its magnificence, lies in New York's 20th Congressional District. So does Saratoga Springs and its renowned racetrack, as do a host of small towns that should make this district quintessential Republican territory. For two decades, the district was represented by conservative stalwart Gerald Soloman, whose vote often topped 70 percent. His Republican successor should have had the seat for life, but a series of bizarre personal incidents enabled centrist Democrat Kirsten Gillibrand to take the seat narrowly in 2006. Earlier this year, Mrs. Gillibrand was appointed to Hillary Rodham Clinton's U.S. Senate...