The main issue is that Clinton is unlikely to maintain her extraordinary popularity through 2016. Her popularity was boosted by her position as Secretary of State, where she remained above domestic political disputes for four years. Perhaps for that reason, most of Clinton’s predecessors, like Condoleezza Rice and Colin Powell, have been broadly popular, as well. As she re-enters the fray and Republicans redirect their attacks away from the president and toward the ’16 Democratic frontrunner, her sky-high favorability rating will probably drop, as it has in the past. For instance, her ratings started out high as First Lady, but dropped when she pursued health care reform. The Monica Lewinsky scandal restored her popularity, but her pursuit of the Senate and Presidency brought her numbers back to earth. Her ratings surged once again after withdrawing from the 2008 presidential primaries.

An Eisenhower-like victory might be more likely if she was winning in a landslide right now—a margin so wide that it would still yield a clear victory, even as her popularity faded and her opponents became better known. But Clinton isn’t winning too many Romney voters. National polls show her around 51 or 52 percent against Republicans other than Christie, while state polls typically show Clinton near Obama’s share of the vote. If Clinton isn’t winning Romney voters at the height of her popularity, there’s cause to be skeptical about whether she will in four years. In the critical battleground states of the Midwest and West, Clinton actually appears to be doing worse than Obama. Not only do recent surveys show her below 50 percent in Colorado and Iowa, but she leads candidates like Rand Paul by just 4 points in Iowa and 3 points in Colorado—worse than Obama’s 5-plus point victories in those states.