House Democrats formally announced the formation of the Medicare for All caucus on Thursday, and were joined by representatives from various progressive groups — like National Nurses United, Social Security Works, and Center for Popular Democracy — who helped save Obamacare last summer and now demand more than the status quo. So far 66 members, or one-third of House Democrats, have joined the caucus led by Reps. Pramila Jayapal (WA), Debbie Dingell (MI), and Keith Ellison (MN)....