The Supreme Court notoriously stopped enforcing the non-delegation doctrine during the New Deal. Since then, Congress has been able to pass laws that grant the executive branch discretionary powers that make parts of it act, in effect, as a legislature.
Conservatives and libertarians are excited at the possibility that the Court is going to revive the doctrine. In a recent case, four justices signaled their interest. A fifth who did not participate, Justice Brett Kavanaugh, is thought to share that interest.
One point that often gets glossed over in discussions of non-delegation is that at no point in American history did we rely primarily on the Supreme Court to enforce it. The Court has only struck down legislation for violating the doctrine twice, both during the New Deal. The prospect of judicial invalidation may have deterred similar legislation previously, but for the most part the principle of non-delegation was enforced through the political process.
That doesn’t mean that the Supreme Court should refrain from ever enforcing the principle. If I recall correctly, Justice Antonin Scalia was wary of the arbitrary line-drawing that robust judicial enforcement would entail but was open to the idea that some such enforcement might be necessary. But it does mean that this is probably an area where constitutional revival will require political, and not judicial, action.