Shapiro contends that "[b]y design, the President must have the freedom to use whatever measures he sees fit in making any and all nominations and appointments." He cites Hamilton in Federalist 76 as saying that the President has the sole discretion in determining who should be nominated for an office, and contends that the Constitution's explicit limit on appointing a sitting Senator or Representative to an executive office also implicitly denies that there are any other limits on who the Executive can nominate.
This is well and good as far as it goes, and I find it persuasive in the case of Senate-confirmable appointments (where the appropriate check on the President's appointment power is the Senate's authority to vote yay or nay on the nomination). But Kushner's position does not demand Senate confirmation. Indeed, what makes this a difficult legal question is that, unlike appointing someone to a cabinet position, a role like Kushner's is not explicitly envisioned in the Constitution (thus making it difficult to glean what the constitutional rule is).
To clarify, let's go to the constitutional text: Article II, Section 2.
[The President] shall have Power, by and with the Advice and Consent of the Senate, to make Treaties, provided two thirds of the Senators present concur; and he shall nominate, and by and with the Advice and Consent of the Senate, shall appoint Ambassadors, other public Ministers and Consuls, Judges of the supreme Court, and all other Officers of the United States, whose Appointments are not herein otherwise provided for, and which shall be established by Law: but the Congress may by Law vest the Appointment of such inferior Officers, as they think proper, in the President alone, in the Courts of Law, or in the Heads of Departments.Kushner's prospective role as a political advisor is not (for reasons not worth getting into) an "Officer of the United States," and so does not need Senate confirmation. If he is an inferior officer, then Congress can decide who gets to appoint him -- the President, the courts, or the heads of departments. Here, of course, it is the President who gets to appoint his chief advisors. But in this context can Congress impose restrictions on who can be appointed?
Possibly. In United States v. Perkins, the Court considered whether Congress could impose restrictions on the removal of an inferior officer whose appointment went through the head of a department. Distinguishing the case of a Senate-confirmable appointee, the Court wrote:
We have no doubt that when Congress, by law, vests the appointment of inferior officers in the heads of Departments it may limit and restrict the power of removal as it deems best for the public interest. The constitutional authority in Congress to thus vest the appointment implies authority to limit, restrict, and regulate the removal by such laws as Congress may enact in relation to the officers so appointed.
The head of a Department has no constitutional prerogative of appointment to offices independently of the legislation of Congress, and by such legislation he must be governed, not only in making appointments but in all that is incident thereto.116 U.S. 483, 485 (1886) (emphasis added).
On the one hand, Perkins is very different from the present case: It is a removal, not an appointments case, and it is departmental rather than an executive appointment. But the italicized language suggests that where an actor has "no constitutional prerogative of appointment" -- that is, where it is up to Congress to decide who gets to make an appointment -- then Congress has the authority to set the conditions upon which the appointment is made. If Kushner is an inferior officer, then, and subject to congressional rules regarding who gets to make the appointment, he may consequently be subject to congressional rules regarding who is allowed to receive the appointment as well.
This, in turn, assumes that Kushner is even an "inferior officer". Inferior officers, the Supreme Court has observed, are those "whose work is directed and supervised at some level by others who were appointed by Presidential nomination with the advice and consent of the Senate." Edmond v. United States, 520 U.S. 651, 663 (1997). A purely political advisor doesn't seem to fit this mold either; there is no Senate-confirmable officer he serves under. And if Kushner wouldn't be a principal or an inferior officer, then there aren't any constitutional rules speaking to his appointment one way or another. This goes to the larger point that the modern executive branch qua branch, with its wide network of aides and advisors, really isn't contemplated in the Constitution at all.
So the question is, for those government officials whose appointment process is not spelled out in the Constitution, is it permissible for Congress to impose certain rules prohibiting nepotism or favoritism? In normal circumstances, I think the answer is yes, but I'm in agreement that the particular case of a close presidential advisor may warrant special attention. The existence of these sorts of advisors is thought to be intrinsic to the functioning of the Presidency as an institution, and it stands to reason that there at least the President must have absolute discretion in deciding who he will and won't receive advice from (this is similar logic to how we get the concept of "executive privilege", which is also unwritten in the Constitution). Under this view, it actually matters a great deal that Kushner won't be receiving a salary: it is one thing to guard against relatives receiving payouts from the public fisc, it's quite another to say that the President is forbidden from getting advice from someone just because he's a relative. Arguably, what matters most in the analysis here is what perks Kushner gets by virtue of his formal White House title that go above and beyond his pre-existing ability to advice the President at the pleasure of the President.
One final observation is worth making, then. Last week I observed that there is, in fact, very little law or regulation that requires good conduct out of our politician -- much less than one might expect. Much of what we take for granted as basic norms political behavior -- including, perhaps, not turning the executive branch into an arm of one's private or familial business -- are just that: norms. They exist because they are accepted to exist and because we don't tolerate departure from them. Which means that when someone tries to test those norms -- not releasing their taxes, indefinitely refusing to confirm a judge, appointing relatives to high-level governmental positions -- they don't enforce themselves. It's up to us to do it.
On this note, it is worth emphasizing just how dangerous the collapse of GOP commitment to nonpartisan constitutional, ethical, and ideological principles witnessed over the past eight years and now culminating in their utter capitulation to Trump is. Oversight doesn't happen unless the overseers decide to make it happen. Congressional checks don't happen unless Congress decides to act as a check. Democratic accountability doesn't happen unless the demos decides to hold people accountable. When these things don't happen, there is very little that formal law and rule can do to prop up what we let down. I get the sense that some people feel comfortable pushing the envelope around our political norms because they believe that nothing truly bad will happen; if things go too far someone will step in and self-correct. This just isn't true, and in many ways the election of Trump is proof of that. People let the conspiratorial conservative id rampage about unchecked because they assumed that it wouldn't really lead to anything too terrible -- surely, it wouldn't actually yield a President Trump. Well it did, because there's no deux ex machina to save us from what we've already proven we're politically willing to tolerate.
* In fact, I think it's all moot because I suspect Shapiro is correct in his prediction that no plaintiff exists with standing who could challenge Kushner's appointment.