Wow, something along these lines seems to come up on a lot of beta sites on the early days (e.g. HSM and its counterpart on Mathematics).
You clearly know more about Politics than I do, so the specifics should be left to someone more in the know than me. But I can bring up some things that are always brought up when this question comes up:
Don't migrate things here that fit in fine over there.
Questions can be on topic on multiple sites. This happens quite a bit. For example, there are questions about physical-chemistry on Chemistry that would be fine on Physics. This is just fine.
If a question is well-received on Politics - or is received decently at all - it should be left there. We had a large problem on HSM when History decided to migrate two questions to us that already had great answers and lots of votes. This led to a meta post on each site, a follow-up months later when someone saw that the versions on HSM hadn't been deleted (we did not accept the migration) and then a post on Meta Stack Exchange about the general situation. Not good. Not good at all.
As such, it accumulated several questions that were more Law than Politics - some fully offtopic and closed, some kinda-offtopic but clearly better answerable by Law experts.
The fully off-topic, closed ones could be migrated here. The kinda-off-topic ones are a bit dubious. There would have to be a clear consensus that a question is better on Law.
I also notice that less than ten law questions were asked on Politics in the last 60 days, meaning that less than ten of those are available for migration (there are more than don't use that tag, preferring international-law or something related, so increasing the total) - perhaps 25 law-related questions. Give or take. It also doesn't seem like the majority have been poorly received. I see a lot of accepted answers.
I have nothing against migrating some questions here. But they would have to be clearly off-topic on Politics, clearly on-topic on Law, less than 60 days old, and good questions (I refer to the "Don't Migrate Crap" policy).