Chuck Blahous, who was appointed by President Obama to be a public trustee of the Social Security and Medicare programs... estimates that at least “$470 billion of the Medicare savings under the ACA scored by CBO through 2021 substitutes for savings required under previous law.” Whether or not you accept his approach depends on whether or not you think that Medicare funds should be segregated from the rest of the budget.
A CBO report in 2009 stated; To describe the full amount of HI (Medicare Hospital Insurance) trust fund savings as both improving the governments ability to pay future Medicare benefits and financing new spending outside of Medicare would essentially double-count a large share of those savings and thus overstate the improvement in the governments fiscal position.
The White House response is not that it isn't true; what they are saying is it's okay because it has been done before. The White House cites a report from the left-leaning Center on Budget and Policy Priorities that says that Republican Congresses engaged in Medicare double-counting with the Balanced Budget Act of 1997 and the Deficit Reduction Act of 2005. And apparently that makes it okay.