I would like some clarification on caucus or primary rules, please

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I don’t understand your comment about federal court.  If you mean the DNC fraud lawsuit, the court’s holding was that, once the Democratic Party chose to adopt and promulgate a rule, it was bound by that rule.  The 15% rule has been adopted, just as was the rule of neutrality that was at issue in the lawsuit.  Therefore, the 15% rule is in effect.

The Democratic Party (unlike the Republican Party) prohibits winner-take-all primaries throughout the process.  Instead, delegates are allocated proportionally.  Some delegates represent a Congressional district, and the allocation is based on the vote in that district.  Additional delegates are allocated based on the overall statewide vote.  At each stage, the allocation is among those candidates receiving at least 15% of the vote in that district or state (with a special rule for what happens if no candidate reaches that threshold).

There’s a practical problem that arises because delegates are human beings who can’t be split up.  In an election for, say, U.S. Senate, a candidate who gets clobbered in one county can still take that one-tenth of the vote there and add it to his or her statewide total.  In a Presidential primary, though, a candidate with one-tenth of the vote in each of ten Congressional districts can’t combine ten tenths of a person into one.  That candidate simply won’t get any delegates.  The votes for that candidate are not reallocated to other candidates, though.

Note, however, that votes for a candidate who misses the 15% threshold in one district still count toward the statewide allocation.  Many states have fairly progressive urban districts and fairly conservative rural ones.  A progressive candidate who gets only 10% of the vote in a conservative district won’t get any of the delegates from that district, but the votes from that district will be counted in determining the statewide allocation.

Interesting , but what happens to the delegate count? Let’s say that a state has 10 delegates. Candidate a gets 50%, B 25%, C,d,e.f, and g each get 5%. Do c,d,e,f,and g’s delegates go to the convention unassigned? And what happens to B? Does he gain or lose his half delegate? My understanding is that caucuses force themselves to decide that at the time, but what about primaries?

Don’t the rules depend on who is ahead, or maybe behind? It sure seems so.

Another reason why turnout, turnout, turnout is so important. The only way to overwhelm the DNC system is with sheer weight of numbers.