One of the most controversial ideas in Washington right now is to turn Medicaid into a block grant program. Republicans say the idea is crucial to lowering the federal budget deficit and would give states needed flexibility over how to run their Medicaid programs. Democrats say it would end up gutting an essential piece of the social safety net. How would block grants change a program that currently serves more than 50 million people? Here's a primer on how Medicaid works, what's being proposed and what the impacts might be.