Donald Trump has been annoyed at the piles of papers and so called facts that have been brought to him regarding healthcare and Obamacare. Many of these facts come from the Congressional Budget Office, which has been in place since Richard Nixon.
The department has numerous employees and a large budget as well. Donald thought we could save on all that by replacing it with his personal CPA, the guy who keeps Trump's taxes well hidden from the public.
Bernie has several points in his favor. Topmost is the fact that he does not present Trump with numbers, instead giving Trump a YES or NO answer to any fiscal decision.
The department may not be so easy to get rid of though, as it serves the Congress and the public, and is not under any cabinet secretary: The Speaker of the House of Representatives and the President pro tempore of the Senate jointly appoint the CBO Director, after considering recommendations from the two budget committees.
Therefore, Trump will be asking the CBO to filter all information to him through Bernie, who will in any case have a nice office in the building.