Editor’s Note: Dean Obeidallah, a former attorney, is the host of SiriusXM radio’s daily program “The Dean Obeidallah Show” and a columnist for The Daily Beast. Follow him @DeanObeidallah. The opinions expressed in this commentary are his own. View more opinion articles on CNN.

CNN  — 

At this point, the question really shouldn’t be which Democrats are running for president, but rather can the few Democrats who are not running please identify themselves? In the last three days, former Housing and Urban Development Secretary Julian Castro formally declared his candidacy, while Rep. Tulsi Gabbard told CNN’s Van Jones that she plans to announce her own candidacy in the coming week.

Meanwhile, last weekend, Sen. Elizabeth Warren was blazing across Iowa meeting voters in that pivotal caucus state, while the media remains on Joe Biden watch to see if and when he will declare.

The list of people who are mulling or clearly about to jump in the race goes on – from Sen. Bernie Sanders to Sen. Kamala Harris. And there are many in between, from better-known potential candidates like Sen. Sherrod Brown and former Rep. Beto O’Rourke to the lesser known, like West Virginia state Sen. Richard Ojeda, former Maryland Rep. John Delaney and the wonky Andrew Yang.

The number of Democratic candidates, like the universe itself, seems to be ever expanding. So, why are we seeing what appears likely to be a staggering number of Democratic candidates declaring in 2020, when they did not to do so in 2016 or even 2008?

Simple: Donald Trump and Hillary Clinton.

Yes, these two politicians, who could not be more different, are the reasons for this mad dash to the Democratic nomination, but for vastly different reasons. In short, it’s because when looking at 2020, Trump is there, and Clinton likely isn’t.

Let me explain. Clearly, Democrats were going to run against Trump regardless of where his approval ratings stood or how strong he was perceived to be in his reelection bid. But Trump’s unpopularity, caused by everything from Robert Mueller’s investigation of the Trump campaign’s possible ties to Russia, to Trump’s non-stop lying and Twitter tantrums, is clearly inviting more to run. He seems, in a word, beatable.

For example, on Sunday, a new CNN poll found Trump’s approval ratings have fallen to an anemic 37% (one of lowest of his presidency), and he now has an astoundingly high 57% disapproval number. And according to Five Thirty Eight’s average of polls, overall Trump now has fallen to a 40.6% approval rating.

Compare this to 1992, when Democrats were looking at taking on then-President George H.W. Bush, who at this point in his presidency boasted a 62% average approval rating, in large part due to the success of the first Iraq War. By August 1991, only one Democrat – then-Massachusetts Sen. Paul Tsongas – had announced a formal run, while much of the news coverage was about big names like then-Sen. Al Gore bowing out of a bid for the presidency.

The sense was Bush was so popular that some Democrats were going to wait until 1996 to run, when they assumed Bush would be leaving office. The lack of big name Democrats in the field in 1992 also helped a relatively unknown Bill Clinton, then governor of Arkansas, capture the nomination.

And speaking of the Clintons, the other reason Democrats are falling over themselves to run is that Hillary does not appear to be a candidate, despite some suggestions to the contrary last year. In 2008, when she first sought the Democratic nomination, given her experience as a first lady and senator, her name recognition and her fundraising ability, she was described by many in the media as the “inevitable” Democratic nominee. While Clinton ultimately lost to Barack Obama, heading into the primary season there were only a few viable Democrats competing against her. No doubt the sense of her “inevitability” scared some Democrats away from running.

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    Once we arrived at 2016, Clinton became even more formidable, given she had served as secretary of state in the Obama administration, and she had the benefit of learning from her 2008 run. In fact, by August 2015, famed polling prognosticator Nate Silver gave her an 85% chance to win the Democratic nomination.The result was that the only Democrats who challenged Clinton in 2016 were the relatively unknown former Maryland Gov. Martin O’Malley and former Virginia Sen. Jim Webb. Clinton’s true challenge in that primary came from Bernie Sanders, who had long identified as an independent but ran as a Democrat in 2016.

    But in 2020 Clinton does not appear likely to be a candidate, leaving Democrats of all varieties and beliefs the option of running and possibly winning the nomination.

    In the coming months, we will likely see even more Democratic candidates announce a run for president. And, as they plead their case to the American people, keep in mind that so much of this is a result of the unlikely duo: Trump and Clinton.