In recent years, there has been a very close connection between voting for presidential candidates and voting for House and Senate candidates. There is less ticket splitting and more party-line voting than at any time since the 1950s. So if either President Obama or the Republican nominee wins a decisive victory in the presidential election, the winning candidate’s party should benefit from a coattail effect in the House and Senate elections.
A decisive Obama victory could help Democrats make substantial gains in the House and help them limit their losses in the Senate while a decisive Republican victory in the presidential election could help Republicans make substantial gains in the Senate and limit their losses in the House. Either of these scenarios could result in a wave election. On the other hand, a very close presidential election could increase the likelihood of a status quo congressional election with only modest Democratic gains in the House and only modest Republican gains in the Senate.
Which makes sense, I think. But it also makes me nervous, because like a lot of others, I think it's important to retake the senate. And having a lackluster field of candidates challenging Obama doesn't make me any less nervous. It may come down to this:
Regardless of who wins the presidential election, though, it is highly unlikely that Democrats will make large enough gains in the House to regain control of that chamber and that Republicans will simultaneously make large enough gains in the Senate to regain control of that chamber. Either one of these scenarios is possible, but the chances of both occurring in the same election are minimal because Senate and House elections are both affected by the same national political forces.
So that's something to add into the calculation: which candidate currently running for president is more likely to achieve a "decisive" victory?