I've been checking the results and early pools of previous presidential primaries for both parties in the last 20 years or so, and it seems that right now, even if there's still 18 months to go, we should have a good idea of who's probably going to win (or at least narrowing the field to a handful of candidates). Anyone with less than some 12-15% (let's make it 10% since the field is so crowded) is a no-go at this point. So that means one among Biden, Sanders, Harris, Warren and O'Rouke (which I'm assuming will go above 10% when he declares his intent to run) are very likely the nominee.
The only exception to this rule was Trump - but then, he didn't declare himself as a candidate until mid 2015, and went to immediately lead the polls or close to it thereafter. I'm willing to discount earlier (90s and 80s) primaries since there was no internet etc. back in the days. But even then, Bill Clinton for instance wasn't the non-entity before 1992 some like to claim when advocating for a surprise or outsider candidate.
It might seem a boring choice, but I'm starting to bet on Biden. He'll run a smooth campaign, based on his experience and moderation, much like Bush and Romney did before, and cruise to the nomination with it.
