T HERE ARE still 65 weeks to go until the Democratic Party holds its nominating convention in Milwaukee—about the same amount of time a rhinoceros pregnancy lasts. Is it too early to say anything meaningful about which candidate will win? Yes it is: at this point in the 2016 cycle Donald Trump had not even announced his bid for the presidency. But although the most widely watched information about the race, public polls, will not help you pick a winner until mid-summer, they can convey useful information about the top-three candidates even this early.

Presidential primaries have changed greatly over the past half-century. It was once relatively easy to identify a winner, as fewer candidates ran and elite endorsements could make or break a campaign with ease. Most candidates did not formally announce they were running unless they already knew they were going to have a good shot at the nomination. The so-called “invisible primary” really was invisible to most Americans. Contests typically had just a handful of candidates and many fewer states used primaries to select a candidate than they do today. The timetable has changed too. William G. Mayer and Andrew E. Busch, two political scientists, calculated that back in 1976 voters had selected only 19% of all delegates by the sixth week of the primary season. By that point in 2020 just shy of 60% will have done so.

Though the process has sped up, it is still possible to tune in too early. Election-watchers querying when to pay attention to the 2020 race have to solve three puzzles. First, they must pick a point when the main candidates can be identified. Second, they have to determine when voters will start making up their minds about which candidates to support. Third, they must factor in when the public will have information at their disposal to shape those intentions. The best single indicator that offers insight into all three questions is public polling.