The Trump Tax cases - what now?

Jay Sekulow, Donald Trump's personal lawyer has petitioned the United States Supreme Court to block a  New York District Attorney from enforcing a subpoena to Trump's accountants for the tax returns of the now President for several years before he took office.

The bete noire is the threat of a President under indictment - though the grand jury subpoena is itself an early stage in a prosecution.  An indictment may or may not follow.  But what seems certain from the relentlessness of Trump's resistance is that bad news will follow.  Trump has engaged in payoffs to the pornographic performer Stephanie Daniels, and other women that landed his personal lawyer Michael Cohen in a federal prison. If the Supreme Court blocks the subpoena it will effectively immunize Mr. Trump from prosecution for such pre-Presidential conduct, and other possible financial misconduct.
The Court of Appeals for the District of Columbia Circuit has refused the Trump request for full en banc review of the panel which ordered his accountants to comply with a Congressional subpoena.  A second petition for certification is sure to follow.
UT Austin professor Steve Vladeck games it out:

1. With two of the subpoenas for @realDonaldTrump's financial records likely to make their way to #SCOTUS in the next 36 hours, I wanted to put together a detailed #thread walking through where we are and what happens next.

Apologies in advance, but this is going to get nerdy.

— Steve Vladeck (@steve_vladeck) November 14, 2019

QUESTIONS PRESENTED (by Trump)

The District Attorney for the County of New York is conducting a criminal investigation that, by his own admission, targets the President of the United States for possible indictment and prosecution during his term in office. As part of that investigation, he  served a grand-jury subpoena on a custodian of the President’s personal records, demanding production  of nearly ten years’ worth of the President’s financial papers and his tax returns. That subpoena is the c ombination—almost a word-for-word copy—of two subpoenas issued by committees of Congress for these same papers. The Second Circuit rejected the President’s claim of immunity and ordered compliance with the subpoena.

The question presented is: Whether this subpoena violates Article II and the Supremacy Clause of the United States Constitution.