For one thing, no one is sure whether Clinton will actually run. She turns 69 in 2016 (the same age as Ronald Reagan when he was first elected in 1980) and she may consider that her achievements in eight years as first lady and U.S. senator and four years as secretary of state are enough for one lifetime.

Her achievements in that last office may look less impressive than they did in the first Obama term when majorities expressed approval of the president’s foreign policy. Clinton’s proudly proclaimed “reset” with Russia suddenly looks less like a triumph than a misfire.

She’s also had health scares: a blood clot behind her right knee in 1998 and another in her skull in December 2012.

The 2016 election will be only the fourth in the last 40 years in which the incumbent president wasn’t running. In the previous three — 1988, 2000, 2008 — the candidate of the president’s party ran roughly in line with the incumbent’s job approval.