The flaws of FPTP voting are generally well known at this point. Extremely popular policies are given no platform in the US two party system. But could a grassroots network of vote compacts negate the spoiler effect?
A big-tent psuedo-party could hold a parallel primary before elections, agreeing to use all votes for a candidate if a critical threshold is reached. A green light candidate would need 51% (+ X% margin) of internal votes and ~40% of total election votes (varying by historical election turnout). Otherwise the voters default to least evil of the two party system.
The first question is legality, which I have no clue on. However, political parties are built on the idea of shared voting power, so I don’t see how any argument against this scheme would make sense.
The second question would be logistics. Validating public voter identities is easy enough, but there would need to be a system of representative conventions to maintain trust. A local group proving unity by winning a local election would grant them access to a higher tier, up to the national level.
Obviously there are more complexities in reality (eg: the US electoral college, real life voter loyalty, etc…), but could it work?
For the average voter it’s not much different than a regular political party: vote for this candidate if we endorse them. The actual math and projections of when to trigger this can be coordinated and agreed on by people you/your local representative trust.
The theory is simple but it probably would be trial and error in practice. For example, if our actual turnout votes for an endorsed candidate differ from our pledged voters by X% then we need to increase our number of pact members proportionally before triggering.