The states need to pass laws stating people can't cross over in the primaries
Are you saying that this is something they might try to do to give a boost to establishment candidates, or is this something you actually want? Because if it's the latter then your opinion is wrong. If it's the former then it would help stop situations where members of the opposite party vote for the candidate further away from the party establishment or base but I think such voting is exaggerated.
We need to stop people from screwing up the other party's primaries.