The conservatives have for years said that congress needed to take more authority, and the executive make less decisions. This is part of a set of scholarship going back to the 70s that decries the administrative state. Believing that if congress is forced to allocate and spend all of the money there would be less expansion in government.
If this clearly fake emergency can stand, when congress has not only not authorized it, but voted to the contrary in an area (spending) that the constitution expressly authorizes is exclusively within the control of congress:
“The Congress shall have Power To lay and collect Taxes, Duties, Imposts and Excises, to pay the Debts and provide for the common Defence and general Welfare of the United States”
“No Money shall be drawn from the Treasury, but in Consequence of Appropriations made by Law . . .”
Then a future president would be able to (a) create a national single payer health care system to address our health care emergency, (b) require the registration and restriction of all guns to address the emergency of gun violence, remove impediments to voting to address the emergency of blocking access to the ballot, etc.
Roberts has enough of a long view that there is no way he would go along. And I would 99% say that Thomas believes too much in the republican doctrine to go along either. Both would be concerned about undermining what little credibility the Court has left. Alito is a hack, to early to tell on Gorsuch or Kavanaugh.
I would bet a lot that Trump would have no more than 3 votes, and perhaps none.