Every presidential election is a response to the current president, even when the current president isn’t seeking re-election. If people don't like the guy in the White House, it’s almost impossible for a member of his party to be elected to succeed him. Even when voters are happy with their incumbent president, it’s not always a guarantee of success for the party’s nominee. Voters are often looking for a change in style as much as substance (see: Bush v. Gore, 2000). This is why we should spend as much time checking in on President Obama’s job approval ratings as we do the polling data of the potential presidential candidates.