State Attorney General Tom Corbett and former Rep. Pat Toomey led a GOP tide in Pennsylvania that mirrored the national surge that carried Republicans to control of the U.S. House of Representatives.

Mr. Toomey had a narrow advantage in most pre-election polling but the Democrat held a surprising lead for much of the night until Mr. Toomey’s strength in the center of the state allowed him to come from behind. In the end, the former Club for Growth leader won his seat by the closest margin of any Pennsylvania Senate race in at least 40 years. Mr. Toomey’s candidacy had forced the incumbent, Sen. Arlen Specter, to flee the Republican Party. His win added to the GOP Senate gains that left them just short of control of that chamber as well.

Pennsylvania Democrats represented a disproportionate share of the party’s congressional casualties. At least six Democratic seats, half of the party’s strength in the state delegation, fell to the GOP. The losses fell heavily on the class of 2006 and 2008, the big surge years for Democrats here and across the county. The losers included Rep. Kathy Dahlkemper, the Erie freshman who fell to Butler auto dealer Mike Kelly. Across the state, other members of the Democrats’ conservative Blue Dog coalition were losing or in unexpectedly tight races. The GOP also picked up two seats in the Philadelphia suburbs and two more in the state’s northeastern corner.