No, each election has different circumstances which in the beginning puts one candidate ahead of another. For example, the 2008 election was heavily favored for whoever the Democratic nominee was after eight years of Bush, who is generally considered a fairly bad President for many different reasons.
Yeah and then you have years like 1984 when the incumbent is extremely popular and so is overwhelmingly the favorite.
The only times it's roughly 50-50 are when there's about equally much going for and against the incumbent party. So I think 2000 and 2016 are both good examples of that, no surprise they're also two of the closest elections in recent years.
