(CNN) -- If Republicans regain control of the Senate on Tuesday night, they will have good reason to gloat. They recruited much stronger, more sensible nominees this year -- no more candidates riding broomsticks or hurling insults at women. They also smartly accepted President Barack Obama's implicit challenge to make his record their centerpiece. But when they wake up from their celebrations, top GOP strategists such as Karl Rove will surely warn them: "Don't over-read this election. Yes, it opens up great opportunities for the next two years, but it does not open a clear path to seizing the White House and Congress in 2016. Beware the 'blue wall!' "
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David Gergen: Whatever happens Tuesday, GOP will face uphill battle in 2016
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Democrats have advantage of a "blue wall" of states with solid record in presidential races
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Democrats can win White House again if they hold blue wall and win Florida, Gergen says
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The political terrain for Republicans will be much tougher in 2016, he says
But they tend to have much smaller populations than the @placeholder states so that they account for only 179 electoral votes -- 91 shy of 270, leaving a huge hill to climb.