At least some of the debate concerns whether or not the President has the prosecutorial (or executive) discretion to do what he says he will do. Josh Blackman argues no, while Ilya Somin argues yes (here and here).
After reading such analyses, I wonder if the fundamental constitutional issue can be simplified. It seems to me that perhaps framing this issue in terms of discretion is off target, or at least discretion is only of indirect concern. Looking at the Constitution I find that "all legislative powers herein granted shall be vested in a Congress," and also "the executive power shall be vested in a President." I think that means there are two separate and distinct powers, and the idea is that Congress does not constitutionally have executive power while the President does not have legislative power.
Therefore, it seems to me the direct constitutional issue is whether or not the President's promised executive order will be exercising the legislative power or the executive power. If it will exercise the legislative power, then the President does not have the constitutional power to take such action.
It seems to me the President has actually answered this question.
Had the House of Representatives allowed that kind of bill a simple yes or no vote, it would have passed with support from both parties. And today it would be the law.If Congress can constitutionally take the action the President says he wants to take, then I say that action falls within the legislative power. The President seems to think this as well since he says if Congress had done what he wants to do, then "it would be the law." It could not constitutionally be law if Congress was acting within the executive power.
Perhaps there is one other way to think about the relevant issue. If Congress had acted to pass a statute that did what the President wants to do, would anyone, including the President, want to assert that the Congress was attempting to exercise the President's executive power. According to the President's speech, he would not make such an assertion.
It seems to me we should conclude the President's promised executive order will be an unconstitutional presidential action because it will be a legislative action.
I want to add a couple of thoughts about the idea of discretion. It seems to me the President must have some discretionary power, but that such discretionary power must be within his proper constitutionally granted executive power. I do not think we want to say that proper discretionary power allows the President to act as though he also had legislative power. Since I have just decided his proposed executive order would be an attempt to exercise a legislative power, I never have to take up the question of whether or not the action is within a proper discretionary exercise of the President's executive power.
Finally, I think more discretion means less rule of law, and vice versa. More discretion means rule by authority, not rule by law. More discretion, or more rule by authority, also seems to me to create greater incentives for corruption within government. Thus, I do not want to try too hard to justify an executive's discretion.