Observers of the 2020 primaries expect a huge crop of Democratic candidates to declare before next February’s Iowa caucuses. History tells us that few of those hopefuls will still be contending for the nomination by mid-March.
Pundits have routinely suggested that the field for the 2020 Democratic Presidential nomination might range upward of a dozen candidates. As of today, January 22, 2019, a total of seven candidates have announced their intention to run — Julian Castro, John Delaney, Tulsi Gabbard, Kirsten Gillibrand, Kamala Harris, Richard Ojeda and Elizabeth Warren. Wikipedia lists another twenty people who have “publicly expressed interest” in running including Joe Biden, Cory Booker, Sherrod Brown, Amy Klobuchar, Michael Bloomberg, Jay Inslee, Beto O’Rourke and Bernie Sanders. The field could certainly exceed a dozen candidates before the Iowa caucuses take place on February 3, 2020.
The Democrats saw eight contenders in the 2004 primary race that was eventually won by John Kerry. Michael Dukakis in 1988 and Barack Obama in 2008 fended off six other competitors in their paths to winning the nomination.
Most of these competitors fell by the wayside early. In 1992, 2004, and 2008 just two candidates remained by March 15th. In 1988 Al Gore and Paul Simon continued their contests against Dukakis until April, while Jesse Jackson maintained his symbolic quest into the Convention .

This drastic winnowing of candidates reflects a variety of forces. All the campaigns compete for funds and staffers. Candidates who fail to make a strong showing in the early races see their access to contributions and staff dry up.
These resource limitations are exacerbated by the need to attract and maintain media attention. While it might be possible to cover a dozen candidates at the outset, media organizations inexorably must target their resources to a much smaller number of candidates deemed “viable” by the press and party professionals.
So while we may see long lists of potential Presidential candidates lining up in Iowa and New Hampshire, it is hard to imagine there being more than three or four candidates remaining in the race after Super Tuesday, March 3rd.
For comparison, here is the equivalent chart for the 2012 and 2016 Republican primaries. Fully seventeen candidates took to the stage in the Republican primary debates in late 2015. By March 15th just three candidates remained standing — Donald Trump, Ted Cruz, and John Kasich. A month later Trump stood alone.

