We live in a world where an increasing number of things that are supposed to be done by the Congress are done by the executive. Treaties are supposed to be approved by the President with the ratification of two thirds of the Senate, but the President makes many agreements on his authority based on a variety of claims. Legislation is supposed to be passed by Congress but agencies do most of the legislating through rulemaking. And wrongdoing by executive officials is generally reviewed by executive officials rather than by congressional impeachment. Some of these actions may be constitutional under the original meaning, but some are not.
Another way that the executive takes action that is supposed to be shared with Congress is through appointments. The Constitution provides that appointments are to be made by the President with the advice and consent of the Senate, but the President often makes appointments on his own. Sometimes this was done through a broad understanding of the Recess Appointments Clause (which a majority fo the Supreme Court accepted, but see here for what I regard as the better view).
At other times, the President makes unilateral appointments of the White House staff on the ground that these staff members – however important their positions seem to be – do not constitute officers of the United States under the Appointments Clause. The reason is that these staff members are said merely to give advice, to engage in nonbinding conversations with officials, or to convey messages from the president to officials – actions that would not involve the exercise of substantial authority and therefore would not implicate the Appointments Clause under the Supreme Court case of Buckley v. Valeo. The public policy problem is that the number of these White House staff members is growing and therefore the power of the federal government is increasingly exercised by people who have not secured the consent of the Senate. Again, some of these actions concerning appointments may be constitutional under the original meaning and some may be unconstitutional.