On Thursday morning, something not at all unusual happened: A Democratic politician announced his candidacy for the presidency.

Wait, wait — it gets less unusual still. The Democrat was a sitting U.S. senator, becoming the seventh member of the Democratic caucus to make such an announcement. If you’re curious, that means that a little more than one out of every seven serving Democratic or independent senators is now running to challenge President Trump in 2020.

There was one semi-unusual component to the announcement by Sen. Michael F. Bennet (D-Colo.). He’s a straight white man, which is rarer in the current Democratic field than it usually is.

Before we dive into that, consider this chart of the number of major candidates in each primary race by day since 2000. Not only are there significantly more candidates than in other recent elections, those candidates got in the race early. At this point in 2016, only six of the eventual 17 candidates had declared (not counting the eventual winner).

The pattern is apparent in the above chart. Once one candidate gets in, it triggers the start of a slow accretion of would-be presidents. In this cycle, that trigger was Sen. Elizabeth Warren (D-Mass.), who declared Dec. 31 of last year. In 2016, it was Sen. Ted Cruz (R-Tex.), who didn’t declare until March. The rate at which candidates got into the race in each of those cycles was similar, it’s just that the 2020 Democrats joined earlier and there were more of them.

Fewer of them, though, were straight white men. Bennet’s addition to the field tipped the majority of the Democratic field to the straight white men who’ve been the overwhelming winners of America’s presidential elections. Before Bennet’s announcement, the 20-person field was split between straight white men and candidates who didn’t fit that descriptor.

At the time, the 2016 Republican field had unusual diversity, with a woman (Carly Fiorina), two Hispanic American senators (Cruz and Sen. Marco Rubio (R-Fla.), a black man (Ben Carson) and former Louisiana governor Bobby Jindal, who is Indian American.

Four of those five candidates were among the five Republicans who were the first to declare their candidacies. You might notice a similar pattern in the 2020 Democratic field: The candidates who weren’t straight white men got in earlier.

We can visualize that. The density of candidates who aren’t straight white men declines over time as more straight white men announce their intention to run.

The only time that the country has elected a nonwhite man to be president was in 2008. Barack Obama announced his candidacy in February 2007 — although, that year, his announcement was relatively late.

Thanks to former Maryland representative John Delaney’s mid-2017 announcement, this particular announcement season has already lasted more than 640 days, far longer than the 2008 Democrats’ 399-day stretch. The latest a major candidate has declared since 2000 was in October of the year before the general election (former Ohio representative Dennis Kucinich). So we may have only five months to go.

One other bit of good news: There are only 39 more Democrats in the Senate who haven’t yet announced their candidacies.