The Republican National Committee is expected to debate a proposal next week that would dramatically shift the balance of power at this summer’s convention — and impose a new rulebook for selecting the party's nominee. The proposal, which will top the agenda during a meeting of the Rules panel at the RNC’s annual spring meeting in Hollywood Beach, Fla., would fundamentally alter how the convention is conducted, further empowering the delegates to determine the course of the proceedings. It amounts to not just a changing of the rules but of the rulebook itself, with far-reaching implications, potentially impacting whether party...