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Hillary Clinton may be the 800-pound gorilla among Democratic presidential candidates for 2016, but Andrew Sullivan thinks she has two big weaknesses:

What are her defining issues? Will she run on Obamacare—ensuring its success? Will she run on climate change? Or protection of entitlements? How would her foreign policy differ from Obama’s? Until we get a sense of where she is headed as far as policy is concerned, she runs the risk of appearing as some kind of large juggernaut that simply has to be elected, well, just because. Maybe being the first woman president would render all these other issues moot. But at some point, she will have to enter the fray. I’m not sure she’s actually fully prepped for that. Her campaigning and speaking skills are not as impressive as Obama’s. But more importantly for me is the inability of her supporters to answer a simple question. I was having dinner with a real Clinton fan the other night, and I actually stumped him (and he’s not easily stumped). What have been Hillary Clinton’s major, signature accomplishments in her long career in public life? What did she achieve in her eight years as First Lady exactly? What stamp did she put on national policy in her time as Senator from New York? What were her defining and singular achievements as secretary-of-state?

I count myself as an admirer of Hillary Clinton, but I agree about this. As first lady, she was the driving force behind health care reform, but that failed miserably. And now that Obamacare has been passed, it’s not an issue big enough to base a campaign on. As senator, she was known for working well across the aisle and being an effective representative for New York, but there are no big legislative victories to her name. And as secretary of state, she once again gained a reputation as diligent and effective, but not as a game changer. John Kerry may or may not end up accomplishing any more than Hillary did, but at least he’s showing some ambition.

And Hillary has another problem too: By 2016 she will have been in the public eye for 24 years. That’s unprecedented. In the modern era, Richard Nixon holds the record for longest time in the public eye—about 20 years—before being elected president.1 The sweet spot is a little less than a decade. Longer than that and people just get tired of you. They want a fresh face. That’s largely what happened to Hillary in 2008, and it could happen again in 2016.

But hey: Records are made to be broken, and presidential candidates don’t always have a big signature issue to run on. Most of them don’t, in fact. For now, Hillary is still the clear front-runner. Until she isn’t, anyway.

1In the political arena, that is. Ronald Reagan was famous for 40 years before he was elected president, but he only became prominent as a national political figure in the early ’60s.