The second impeachment Article that the House of Representatives will vote on tomorrow alleges that as part of the “impeachment inquiry, the Committees undertaking the investigation served subpoenas seeking documents and testimony deemed vital to the inquiry from various Executive Branch agencies and offices, and current and former officials,” but that in “response, without lawful cause or excuse, President Trump directed Executive Branch agencies, offices, and officials not to comply with those subpoenas.”  The article goes on to list specific instances of this conduct.
The illegality of the President’s actions in this regard is abundantly clear. 2 U.S. Code §192 provides,
“Every person who having been summoned as a witness by the authority of either House of Congress to give testimony or to produce papers upon any matter under inquiry before either House, or any joint committee established by a joint or concurrent resolution of the two Houses of Congress, or any committee of either House of Congress, willfully makes default, or who, having appeared, refuses to answer any question pertinent to the question under inquiry, shall be deemed guilty of a misdemeanor, punishable by a fine of not more than $1,000 nor less than $100 and imprisonment in a common jail for not less than one month nor more than twelve months.” 
And 18 U.S. Code §2 says,
“(a) Whoever commits an offense against the United States or aids, abets, counsels, commands, induces or procures its commission, is punishable as a principal.
“(b) Whoever willfully causes an act to be done which if directly performed by him or another would be an offense against the United States, is punishable as a principal.” 
Since the president ordered his subordinates to ignore congressional subpoenas, this looks like a slam dunk. Of course, it’s beginning to look as though the Republican majority Senate isn’t going to convict Mr. Trump no matter what the evidence.
But there is an additional complication: executive privilege. Mr. Trump’s defense, to the extent he is required to put on one, will be that the subpoenas sought information that he should be permitted to keep confidential as the President.
The only time the Supreme Court has ever weighed in on the issue of executive privilege was in United States v. Nixon.  That case involved a judicial subpoena in a criminal matter, but the privilege to be claimed is the same. There the Court said that “neither the doctrine of separation of powers, nor the need for confidentiality of high-level communications, without more, can sustain an absolute, unqualified Presidential privilege of immunity from judicial process under all circumstances,” and that “when the privilege depends solely on the broad, undifferentiated claim of public interest in the confidentiality of such conversations, a confrontation with other values arises.” (Id, p. 706) It is difficult to see how it could be any different with a congressional subpoena.
Now all of this is, doubtlessly, an academic exercise. The Republican led Senate is not going to remove the Republican President from office.
Meanwhile, Mr. Trump recently had to pay “$2 million to eight charities as part of a settlement in which the president admitted he misused funds raised by the Donald J. Trump Foundation to promote his presidential bid and pay off business debts….In the end, the president admitted in court documents that he had used the foundation to settle legal obligations of his businesses and even to purchase a portrait of himself.”  In other words, he embezzled from his charity.
Why this was not made the basis of another article of impeachment is beyond the grasp of your humble servant. From the public perception standpoint, refusing to cooperate with Congress is one thing; stealing from a charity is quite another. The spectacle of the Senate trying to summarily dismiss an impeachment article like that would raise a stench reaching to the far reaches of the solar system.
One supposes that the defense would be raised that Mr. Trump committed his misdeeds in connection with that case before he was President, so it doesn’t count. That theory, of course, would immunize a president from impeachment even if old bodies were dug out of his backyard, so it wouldn’t need to be taken seriously.
It is apparently apocryphal that the curse “may you live in interesting times” is of Chinese origin. But we live in them all the same.