Sez here Barr can block any Contempt of Congress citations.

[dixiegrrrrl]

Following a contempt citation, the presiding officer of the chamber is instructed to refer the matter to the U.S. Attorney for the District of Columbia;
according to the law it is the "duty" of the U.S. Attorney to refer the matter to a grand jury for action.
However, while the law places the duty on the U.S. Attorney to impanel a grand jury for action, some proponents of the unitary executive theory argue that the Congress cannot properly compel the U.S. Attorney to take this action against the Executive Branch, asserting that the U.S. Attorney is a member of the Executive Branch who ultimately reports only to the President and that compelling the U.S. Attorney amounts to compelling the President himself.
They argue that to allow Congress to force the President to take action against a subordinate following his directives would be a violation of the separation of powers and infringe on the power of the Executive branch. The legal basis for this position, they contend, can be found in Federalist 49, in which James Madison wrote “The several departments being perfectly co-ordinate by the terms of their common commission, none of them, it is evident, can pretend to an exclusive or superior right of settling the boundaries between their respective powers.” This approach to government is commonly known as "departmentalism” or “coordinate construction”

Others argue that Article II of the Constitution requires the President to execute the law, such law being what the lawmaker (e.g. Congress, in the case of statutory contempt) says it is (per Article I).
The Executive Branch cannot either define the meaning of the law (such powers of legislation being reserved to Congress) or interpret the law (such powers being reserved to the several Federal Courts). They argue that any attempt by the Executive to define or interpret the law would be a violation of the separation of powers; the Executive may only—and is obligated to—execute the law consistent with its definition and interpretation; and if the law specifies a duty on one of the President's subordinates, then the President must "take care" to see that the duty specified in the law is executed. To avoid or neglect the performance of this duty would not be faithful execution of the law, and would thus be a violation of the separation of powers, which the Congress and the Courts have several options to remedy.

https://en.wikipedia.org/wiki/Contempt_of_Congress#Procedures

So this means 2 things:
1.
The US Attorney General, who is Barr at the moment, has the power to tell any US Attorney to not prosecute a case.
The US Attorney for the District of Columbia is Jessie K. Liu, oppointed by Trump.

2. Trump/WH will sue, arguing the unitary executive theory. As Trump said publicly a month or so ago, they will sue, and if they lose, they will appeal all the way to the top.
The chief judge of the United States Court of Appeals for the District of Columbia Circuit is....Merrick Garland.