Most localities in the US are dominated by one of the major parties to the point where the primary becomes the election. That doesn't leave any room for a third party to break in either. Too many people never learn about local candidates and end up just pulling a straight ticket lever.

This is the end result of decades of gerrymandering.

I wonder if you could form a mathematical model of which districts would be most amenable to a dedicated 3rd party challenger. It seems like you'd want a district which is a "safe seat" (if there is a serious R/D contest in the district, people will want to avoid "throwing away their votes" by voting for a 3rd party). But you'd also want to identify a district where people are dissatisfied with their elected representative anyways. Ideally the elected representative is a significant distance from the median voter.

Maybe a good metric would be the ratio of primary ballots cast to general election ballots cast. If a small number of extremist primary voters are de facto selecting the candidate that will win the general and get the "safe seat", that suggests an opportunity for disruption by being a high profile 3rd party candidate who's just a bit more moderate than candidates the extremists select (more appealing to the median voter).

Another idea is to reach out to a bunch of independent candidates and try to recruit them for your new party to work towards critical mass.

Really the big issue here is not lack of ability but lack of will.

Look at the Tea Party and the DSA; they have enough motivated bases to form parties of their own, but their strategy is to co-opt and purify the existing mainstream parties. Equivalent movements in Spain decided to make their own parties and Podemos and Vox became the next two largest parties in Spanish elections.

If you run a third party that is appealing enough, you can certainly have a go at it. I just have literally never seen, I don't know, the Green Party put up a candidate for local city elections.

It's not like party establishments haven't had candidates lose despite all odds. And Independents have had good streaks at lower offices (e.g. Bernie Sanders, Michael Bloomberg)

Depends where you are: In the recent California governor recall, there were two Green Party candidates and one Libertarian.

Governor is already a bit high-level to really have a chance at breaking through, isn't it? Or am I misunderstanding what you mean?

Was responding to the idea that the Green party doesn't put up candidates for local elections... I think I've seen them on smaller races than Governor as well, but this was a recent example that came to mind easily.

Just curious, but how strong are those campaigns actually? Do they do the door-knocking, the ads, and the voter registration?

Not in my experience.

I wonder if it's seen as a necessary evil for perceived relevance. If you aren't running a presidential candidate, it feels like an admission that you're a local player without the resources to run a big, expensive campaign.

I wonder if there's anything to be learned from those weird "secondary" parties you see in some states. It will be like "Working Families Party" or whatever, with a Democratic or Republican candidate for President and few unique of down-ballot names.

I'm not sure exactly how those work. Might be just a way to use some legacy "default ballot access" In my state, a candidate supplied by any of the four largest parties would get on the ballot, even if only 15 people actually voted for the Green or Libertarian.

Perceived relevance hardly matters if you never win seats, though.

Electoral margins, particularly in downballot elections, are very very slim. For City Council of New York, which is a fairly powerful local position, you are looking at margins in the hundreds or thousands of voters, and combined with how thin legislative majorities tend to be, can form a significant wedge to wield.