It works like this: Imagine you’re publicly considering a presidential bid, or that you’re the focus of serious speculation about it. You decide not to run, but your party then goes on to lose. The following election, then, is almost always doubly tricky for you if you want to run.

“One of the few universal truths in politics is that it’s about the right person with the right message at the right moment in history, and there’s no formula for figuring out who that is, or when that is, until it’s in front of you,” explained longtime Democratic strategist Mo Elleithee, who now runs Georgetown’s Institute of Politics and Public Service. Elleithee worked for Hillary Clinton in 2008, on an unsuccessful campaign that was — early on — followed by occasional questions about whether she should have jumped into 2004’s fray.

It’s delicate ground to tread. First, there’s the potential fear that you’ve missed your moment to succeed, for whatever reason: Maybe the state of your opposition has changed, your own career has stalled, external factors — say, the economy — have shifted and now favor you less, and so on. Then, there’s the difficulty of running an entirely new race without succumbing to the temptation of fighting the last one’s strategic battles. And finally, there’s the challenge of convincing the public — which knows you considered running last time — that your campaign really is about the future, not trying to lay belated claim to what might have been yours four years ago.