By entering the 2020 Democratic nomination battle, it means that Joe Biden now has 19 rivals gunning for him, but the massive size of the field could play to his benefit.

In general, the more crowded a field is, the more difficult it is for candidates to break out and get the attention of the media and of voters. But as a former vice president with essentially universal name recognition, Biden is guaranteed to receive tons of media attention for what he says and does in a way that his rivals will not. That will make it more challenging for other candidates to gain ground, and as long as he remains on top of polls, it will only reinforce the media's focus on him.

We saw a similar scenario play out in the 2016 Republican race. As a widely known celebrity with a penchant for going off-script and making wild comments, Donald Trump was able to absolutely dominate coverage in a Republican field with 17 candidates. That made it extremely difficult for other candidates to get their message across or gain any sort of momentum. Whether people liked or hated what Trump was saying, whatever Trump was saying was always the issue that was being debated. This frustrated his rivals, who lamented that the media treated the race as if there were no other candidate. This essentially locked in place a status quo in which Trump dominated the polls.

[Related: Biden voted to give Robert E. Lee his US citizenship]

Instead of attacking Trump, rivals attacked each other, assuming that once the race were isolated into him and an anti-Trump candidate, the anti-Trump candidate would finally be able to consolidate support. Of course, it didn't work out that way.

The situations are not exactly the same for Democrats in 2020, as they never are in politics, but there are some parallels. Biden has been leading in polls and is theoretically vulnerable, but now he's in the race, and for better or worse, he's going to be taking a lot of attention away from the other candidates. There is also a tremendous amount of competition to embrace radical policy ideas to appeal to the resurgent Left, while Biden faces less competition for traditional liberal voters who consider themselves more moderate, both ideologically and in their temperament toward Republicans.

There are plenty of other things that cut against Biden (his age, past policy stances putting him at odds with the modern party, propensity for gaffes, etc.), and they may prove more influential, but the size of the field should be one factor that works in his favor.

[Also read: McCain family to support Biden in 2020 race in bid to defeat Trump]