Mueller on Congressional authority

In the "Constitutional defenses" of the Executive Summary Mueller states the following:

"With respect to whether the President can be found to have obstructed justice by exercising his powers under Article II of the Constitution, we concluded that Congress has authority to prohibit a President's corrupt use of his authority in order to protect the integrity of the administration of justice. […] The conclusion that Congress may apply the obstruction laws to the President's corrupt exercise of the powers of office accords with our constitutional system of checks and balances and the principle that no person is above the law."

It seems Mueller intended for Congress to decide on obstruction, not the Justice Department.