I am not from USA and pertaining to some question I am trying to address, I was curious about how the Presidential candidates are selected or shortlisted for Primaries and Caucuses. Because it's not that if a 1000 people want to run for President, they all would appear as options in ballot in Primaries or in Caucuses. That would be neither practical nor desirable.
If one could also answer this for state level, that would be a bonus for me.
Thanks
It varies from State to State, and even within a State, the rules might be different for different parties.
Generally candidates will either petition (collect signatures), pay a filing fee, or be nominated by a party process.
So in Kansas, the Republican, Democrat and Libertarian Parties determine the candidates in the Primary elections.
In New Hampshire, there is a $1000 filing fee.
In Illinois, 3000 signatures are required.
Other states have a combination: Perhaps a certain number of signatures and a fee, or in Massachusetts. Where the Secretary of the Commonwealth can "place candidates on the ballot who have been generally advocated or recognized in the national news media."
In Iowa and other "caucus" states, the groups emerge in the caucus meetings. THere are no printed ballots, so there isn't a need to "file".
There is a secondary question: How does a party become recognised by the State as requiring Primary Elections. There is usually a restriction on this too. In some states the "Democrat" and "Republican" parties are the only recognised Primary parties, in others it is any Party with a certain level of representation in the State Legislature.
See https://ballotpedia.org/Ballot_access_for_presidential_candidates
Rules will vary state to state, but most (if not all) states will require a minimum number of people to sign a nomination form for each candidate. Only candidates that are able to organise reasonably efficiently will be able to reach that threshold.
They aren't really, which is why recent presidential primary debates have needed comically large stages, or even had to split the field of hopefuls in half and go over two days.
As a lot of other answers have mentioned, there are filing fees and requirements in all 50 states. For someone running for funzies I suppose that could add up to a lot of money and work, but for a serious national candidate these are nominal hurdles.
However, the real gate the last couple of cycles has been the party-sponsored televised primary debates.
To keep the debates manageable the entities running them (the associated party's national committees) have had to institute gating mechanisms lately. This usually boils down to having enough donors to plausibly compete in upcoming primaries, and meeting some polling threshold.
For the 2020 Democratic primary debates, to get in the first debate a candidate had to poll at 1% or better nationally in at least 3 polls, or have at least 65,000 donors across 20 states. These thresholds were moved higher as the debates went on (after the first caucus), to avoid wasting everyone's time with unviable candidates. Of course candidates who just barely didn't make the cut complained bitterly about this.
Similarly, back in 2015/16 the Republican primary debates started with 17 cadidates, split into a main 10, and a 7 person "kid's table" debate. The 10 were apparently picked for being the 10 highest polling, and the 7 based on some typically murky critera. As the primary campaign wore on, the critera were progressively tightened until at the end there were only 3 invitees.
