WASHINGTON — The incumbent senator from Alaska is taken by surprise in a primary. A new conservative movement energizes Republicans in a furious response to a Democratic White House. Little-known insurgent candidates prepare to storm the Senate. It is starting to feel like 1980. While the 1994 Republican takeover of the House is regularly explored for insight into what might happen this polarized election year, parallels are emerging between the watershed Senate election of three decades ago and the campaign of 2010 as another conservative rebellion threatens to reshape the Senate. In 1980, shocked Senate Democrats lost 12 seats in...