Support for multiple candidates is a strength, not a weakness.
The US conservative, corporate media love to claim that because the Democratic Party has numerous candidates, that shows weakness and division in the Party.
This simple meme ignores actual history as recent as 2016, where the GOP had over a dozen deeply flawed candidates, but the same conservative media never stated that this indicated any weakness or division in the GOP.
The Democratic Party is a big tent Party, and the big tent has room for multiple candidates. Not all Democrats support all of the same policies, but this is called diversity.
The GOP, by contrast, is the Party of racism, and greed, and climate denial, and Trump.
Unfortunately, because the US media is 90% owned by conservatives, the GOP will always receive favorable coverage. But 2018 showed that an energized electorate will overcome this media bias, and the structural advantage of the GOP.
If typical Democratic voters actually voted at levels of the typical GOP voters, 2010 would never have happened, and President Obama could have done much more.
So the challenge for Democrats is to energize the base using appeals to reason, rather than the fear based appeals of the GOP.