The primary schedule is made for big money campaigns that can time their momentum for February.
https://www.thegreenpapers.com/P20/ccad.phtml
Basically, there is the usual NH/IA/SC/NV stuff followed by an Ultra-super Tuesday in which Texas and California and a bunch of other good size states all go and more than a third of the delegates are chosen and then a compressed cycle with another third chosen in the rest of March. More than 70% by the end of March.
For candidates other than Bernie and Biden, who start with money and enough support to get them in any top tier, that means winnowing the field between now and January. If there are still more than a half-dozen standing in January, beating either of those front runners will be hard because they'll all split the vote fighting for second or third and a chance to go one-on-one in later primaries with the big guys while the big two rack up delegates.
I don't want Bernie and am kind of meh about Biden, so my hope is both of them start looking like yesterday's news by fall. I think that is possible, in which case we have a race. But if those two are still out front in November it is going to be tough for anyone else.
There is another potential odd dynamic - what if we get one or more "favorite son" candidates who say, hey, Texas, or hey, Calfornia, give me your votes and I'll broker the convention. If Beto takes Texas and Harris California, we could have a dynamic we haven't really seen in many decades.
