Republicans need six new seats to control the Senate. Strategies to get there include:
1. Win the three easy ones. Republicans are heavily favored to replace retiring Democratic senators in West Virginia, South Dakota and Montana, states that President Barack Obama lost by 13 percentage points or more.
2. Go after Democratic senators in four states Obama lost. These incumbents are trying to hold on in Arkansas, Louisiana and Alaska, which Obama lost badly, and in North Carolina, which he lost narrowly in 2012.
Two of these senators — Mary Landrieu of Louisiana and Mark Pryor of Arkansas — are battle-tested winners of multiple campaigns. The other two are first-termers.
3. Don't lose any GOP-held seats. Democrats are making credible bids to win Georgia's open seat and oust five-term Sen. Mitch McConnell of Kentucky, the Republicans' Senate leader. An upstart independent has rattled Sen. Pat Roberts, R-Kansas. All three states went firmly against Obama, and Democratic victories would be upsets.
4. Pick up an open seat in a Democratic-leaning state. Democratic senators are retiring in Iowa and Michigan, which Obama carried twice. Republicans are making credible bids, especially in Iowa, where the Democratic nominee has had some stumbles.
5. Knock off a Democratic senator in a state Obama won. This should be the Republicans' toughest task, but GOP Rep. Cory Gardner is running hard against Sen. Mark Udall, D-Colorado. A longer shot for Republicans is Scott Brown's bid to topple Sen. Jeanne Shaheen, D-N.H.