I’m not saying who wins the presidential contest is meaningless. The executive branch has a lot of discretion to make unilateral decisions. In addition, the bully pulpit can be a powerful tool for setting the debate or changing popular opinion. Who wins the White House will have a real impact on some policies, but as a country we are likely to see truly significantly shifts only if one party wins full control of Washington this election.
As it currently stands, Democrats are in a solid position to narrowly hold onto control of the Senate, while Republicans are likely to keep control of the House. A big win for Mitt Romney could have enough of a coattail effect to help Republicans take control of the Senate, while a very large win for President Obama might help Democrats take the House. A close Presidential election, though, is most likely to leave Congress in its current divided state.
The deals a Republican president would negotiate with a Democratic Senate will be different from the deals a Democratic president will reach with a Republican-controlled House, but the difference in policy outcomes will be likely small compared to what we would get from unified Republican or Democratic government.
The close election may have gotten more interesting to watch but is less likely to produce significant policy changes.