While the Republicans easily took the Senate in 2014, they do not have the same advantage in the 2016 election cycle, according to political analyst Charlie Cook.
The Senate seats Republicans won in the 2014 midterm elections were made to order: there were seven Democratic senators who were from states that former presidential candidate Mitt Romney won handily in 2012, an unpopular president to run against, and very few of their own seats that they needed to defend,
Cook wrote in a report for the National Journal.
That will not be the case in 2016, he says.
Republicans have 24 seats that will need to be defended, while Democrats only have 10. All 10 Democratic Senate seats are all in states that President Barack Obama won in 2012, and seven states that are held by Republicans.
Those states are Florida, Illinois, Iowa, New Hampshire, Ohio, Pennsylvania and Wisconsin.
One silver lining for Republicans is that the Senate seats up for re-election in blue states were not won by Obama by margins that were as wide as the red states won by Romney, where Democrats were up for re-election in 2014.
The reddest state with a Democratic senator up for re-election in 2014 was West Virginia, which Romney won by 27 points in 2012. By contrast, the bluest state up for re-election with a Republican senator is Illinois, which Obama won by 17 points.
Another silver lining for the GOP is that not all states with Republican senators up for re-election that were won by Obama in 2012 are necessarily competitive.
For example, it is very unlikely that Republican Sen. Chuck Grassley will lose in Iowa, even though the president won the Hawkeye State by 6 points in 2012.
In addition, the competitiveness of the other states will depend on who the Democratic challengers are.
Democrats and Republicans may break even on open seats up for re-election — the Democrats have three open seats with two that are in deep blue states, while the Republicans have two open seats, with only one that is considered competitive.
If Democrats want to reclaim the majority in the Senate, they will need to pick up four seats if a Democrat wins the presidential election, and five, if they don't.