I suppose it could mean voting in people to write a law that makes it exceedingly unattractive for institutional investors to buy single family homes. You could probably even do such a thing "neutrally" since people really only need one home and if you own more than two you're almost certainly investing in some way. Apply some onerous tax on each unit owned above 100, and all these investors will flee the market.
Edit: IIRC, the companies that buy up all these single family homes are large corporations. I'm pretty sure you could write a law like I described that they wouldn't try to use some cheeky corporate shell game to try to bypass (e.g. in their tax filings require them to declare how many single family homes they're the beneficiary owner of, regardless of any intermediary shell companies/special purpose entities, and tax them for that). Require the auditors to sign off of on the number. If they lie, everyone's subject to even more onerous civil and criminal penalties (e.g. blow them up like Enron). Large corporations will stretch the law as far as they can, but it's rare for them to deliberately venture into fraud and other kinds of illegality (for the pedants out there, note I said rare not never). The systemic issues can be solved if they're made to comply, even if some relatively small fish still don't
