The GOP will probably need to capture six Democratic seats in 2014 to grab the majority, as Newark mayor Cory Booker is well positioned to win the seat held by interim Sen. Jeff Chiesa (R-N.J.) in a special election. Democrats hold a 54 to 46 advantage, counting two independents who caucus with them.
But they must also defend four vulnerable incumbents and the seat soon to be vacated by Sen. Tom Harkin (D) in Iowa, a swing state.
Sens. Mark Pryor and Mark Begich, Democrats from Arkansas and Alaska, where Obama lost badly in 2012, are in greatest danger. Sens. Mary Landrieu (D-La.), a three-term survivor perpetually on the GOP target list, and Kay Hagan (D-N.C.), who had a solid lead in a recent Public Policy Polling survey, will also have competitive races.
Pryor is seen as the most vulnerable, though Begich is a close second.
The Arkansan has taken hits from the right and the left this year as the anti-tax group Club For Growth and Mayors Against Illegal Guns, have aired attack ads against him. A late-June poll commissioned by the Senate Conservatives Fund showed him in a dead heat with freshman Rep. Tom Cotton (R-Ark.).
Senate Republicans, left dispirited after a net loss of two seats in 2012, now feel a gust of optimism.