While I am no fan of the administration, I will say that Mulvaney does have a point when he says: "it’ll be very difficult” to balance the budget in future proposal without cutting back the growth of Medicare and Social Security" Eventually, something had to yield in the mad dash for spending that happened in the Obama years. While it was necessary for economic stability, just like with the Fed and QE I, II, and III, there comes a time when the throttle on spending has to be pulled back. So Mulvaney says "do it now or your choices are going to be even more politically toxic in future years. 

Something to think about - of course putting aside the knee-jerk reaction of many who call this budget mean and hard - those are emotional words which we have a boatload of in this current political discourse.