Other states couldn’t care less what the Iowa constitution says on the matter.
In practice it’s ultimately up to the DNC (this is a party process after all). In the past if a state threatened to disobey the party the party would just say the state’s delegates wouldn’t count or would count for less. Iowa’s constitution has no governance over DNC policies and practices which at the end of the day are a private matter.
> Not sure how you can change that without having them change that law.
You can change by having either of the national parties set rules about primary/caucus timing and declaring that they won't seat delegates chosen out of line with those rules.
Heck, the whole reason Iowa has to report more dimensions of data this year is a DNC rule (not on timing, obviously) adopted in response to complaints about the results last cycle. So we know the party committees rules do direct the administration of state nominating contests.
This is a state law, not federal. Iowa state law has no standing over other states. If the DNC decides Nevada would be first, what options does Iowa have?
Legally what would happen is any time another state moves in front of Iowa the date for the Iowa caucuses would move up. The power is actually the other way around the DNC has to get Iowa to give up and revoke/ignore the law in their own state to put another state in front of/with Iowa. Any state can move their own date around the best the DNC can do is maybe refuse to acknowledge delegates from states that skip the line but that's a very big button to press.
> It's up to each party to set the rules on how delegates can be selected, including time, place, and manner.
It seems that Iowa chose both, the time and the manner, itself[1]:
> Because Iowa had a complex process of precinct caucuses, county conventions, district conventions, and a state convention, they chose to start early. In 1972, Iowa was the first state to hold its Democratic caucus, and it had the first Republican caucus four years later.
> Under Iowa law, political parties are required to hold caucuses every two years to select delegates to county conventions and party committees.
And each party must respect the laws of the state.
> It seems that Iowa chose both, the time and the manner, itself
Well, no, not entirely. Yes, the parties gave them lots of room initially, but that has evolved. The entire reason they were using the app at issue this year is because after complaints about apparent inconsistencies in the results based on internal reports (there was previously no official tally of the intermediate steps), the DNC directed that to the Iowa Democratic Party must adapt the method so that there were official, reported tallies of the first and second alignments as well as the state delegate equivalent count that is the final result. That is, the national party chose (in a very limited way, for now) to exercise it's fairly absolute power to direct the manner by which delegates to it's nominating conventions are selected. (Aside from this specific intervention, the DNC also has extensive general rules adopted for the delegate selection process, see, for 2020, generally Regulation 4 of the Regulations of the Rules and Bylaws Committee for the 2020 Democratic National Convention.
There is nothing stopping the DNC from making much more exacting requirements, including setting a required schedule or prohibiting the use of caucuses entirely.
> And each party must respect the laws of the state.
Each party has an incentive to do so to avoid conflict with interest groups in the state, but state governments have basically no compulsory power to direct how party national committees allow delegates to nominating conventions to be selected from their state.
Since Iowa holds a caucus, not a primary, it does not apply to New Hampshire's law. Iowa's law says the caucus must be "[a]t least eight days earlier than the scheduled date for any state meeting, caucus, or primary that constitutes the first determining stage of the presidential nominating process in any other state." New Hampshire requires "7 days or more immediately preceding the date on which any other state shall hold a similar election." Apparently the caucus is not considered a similar election.
