How did the design of Medicare satisfy the two competing economic protagonists, namely, the AFL-CIO unions and the AMA? Why was Medicare Part A financed by a regressive payroll tax and Medicare Part B...

How did the design of Medicare satisfy the two competing economic protagonists, namely, the AFL-CIO unions and the AMA?

Why was Medicare Part A financed by a regressive payroll tax and Medicare Part B financed through a progressive tax, namely general tax revenues?