Why don't we just hold all the primaries now?

I've never understood, as a non-American, why they can't all be on the same day.  All other elections are, why not this one?  Have one big national election campaign with THE primary election at the end of it, have a breather, then same again leading up to November.

Or how about going more radical.  The USA is the only country I know that has primaries.  The UK is pretty typical of others and what parties do here is choose a party leader, who will be their candidate to be Prime Minister at the next general election.  They each have their own method but it normally involves a postal vote of all party members, so those of us who haven't paid a subscription to join a party don't get involved.  They do this as and when so there's always a party leader in place.  For example, Labour has just chosen a new leader after the last one led them to the worst defeat since 1935.  He had to go!

So there is always a leader that the actual party has elected, which means the primary bit is done and we can have a general election at any time.  And a snap election is not unusual.  Parliament has to vote to have one but if it does, we can do it in six weeks flat.  As happened at the end of last year.  The Act for an early election was passed on 31 October, Parliament tidied up remaining business and was dissolved by the Queen on 6 November, nominations closed 8 days later, the usual mad month of campaigning occurred followed by the election on 12 December.  Having only a week for formal nominations works because the parties know the timetable and always have candidates in place for all 650 constituencies.  (It's a parliamentary system - we elect the House of Commons and whichever party wins most seats becomes the government with their leader as Prime Minister.)

A US presidential election can't be put on hold because it MUST take place every 4 years in accordance with the constitution.

The primaries are over. It's Trump vs Biden in November. We already know where they both stand, so no debate is necessary.

thats up to trump to decide