If you thought the 2016 GOP presidential candidate field was large, just wait for the 2020 Democrats.  Some observers of the ongoing process believe that "20 or 30" candidates are in the mix already, although few believe that when things shake out, there will be that many.

Politico's David Siders believes that the announced, unannounced, and potential candidates are leading to a convulsion of the party.

In just one convulsive 24-hour period, Democrats got a glimpse of the primary election to come, a precursor to a year of volatility in the party's historic, sprawling 2020 presidential field.

Yet the departure of two candidates – and another seeming to suggest his intention to run – failed to provide any more clarity or definition to the field on the eve of a period in which many candidates have said they will announce their intentions.

"This is like rats in a Skinner maze," said Hank Sheinkopf, a longtime Democratic strategist based in New York.  "Who gets to the end is a function of who has the best luck, who has the most money and who doesn't anger the media."

The Democratic primary field is shaping up to be so large and fluid that the loss of one former governor, Patrick, barely makes a dent – there are still six other current or former governors in the mix.  Avenatti's exit Tuesday removes an outsider and a ferocious Trump critic, but that's also a lane that few expect will be unoccupied when the field is set.  As for Biden, the former vice president and early frontrunner in national polls, his tease generated heat but without providing much light on his thinking about entering the race.

Deval Patrick, a two-term black governor in a very blue state, never got much traction to begin with.  But there were many Democrats who saw an Avenatti candidacy as serious.  The notorious porn star lawyer's sneering, visceral hatred of Trump mirrored the feelings of many Democrats, who saw his path to the nomination as similar to that of the current president.

While Democrats subtracted two candidates this week, they added a couple more:

In the latest expression of Democrats' post-midterm euphoria, Colorado Public Radio reported this week that Sen. Michael Bennet (D-Colo.) is "seriously thinking" about a 2020 campaign.  Sen. Bob Casey (D-Pa.), who didn't register on the 2020 radar until his decisive reelection win in November, said recently that he is "open to all possibilities."

"There's so many names now ... You wonder who's really serious and who's doing it just for getting a higher bump in exposure for something down the road, be it a TV host, a radio syndication, a book deal," said Matt Barron, a Massachusetts-based political consultant who worked on the presidential campaigns of Barack Obama and John Kerry.

Barron said the breadth of the field – and tumult within it – presents an opportunity to lower-profile candidates, potentially explaining why Bennet, Casey or any number of Democrats might not rule out a campaign.

With a larger field, he said, "If someone can win with a smaller piece of the pie, then mathematically it seems to be easier … In a large field, they just need a smaller slice."

All it takes is one or two debates where a minor candidate makes a splash to overturn conventional wisdom and propel a relative unknown into frontrunner status.  With potentially 15 people on the debate stage at a time, the fireworks will begin early, as we saw with the GOP debates in 2016.

It should be noted that a candidate like Beto O'Rourke or Alexandria Ocasio-Cortez will have a huge advantage in grassroots enthusiasm.  That doesn't always translate into primary wins, but it's more likely to keep a candidate in the race, hoping to catch lightning in a bottle.

The upshot to all this candidate-churning is that the 2020 Democratic nomination for president is anyone's race at this point and that the rise and fall of several candidates will change the party in ways that we can only dimly perceive.