Well, they could, but if they have been ordered by subpeona to testify, they could go to jail for it.
Trump could in theory then pardon that, but he’d have to keep reissuing pardons. You cannot pardon something that was done in the future.
And baldfaced bullshitting is all they’re going to do because they wouldn’t begin to know how to function any other way. Most presidents who know nothing about being president usually hire experts who can help them navigate the labyrinth of the federal government and the legal system under the constitution. They do this because they value these institutions, the system, and our constitutional framework. Trump does not. He deals with complexity by taking a sledgehammer to it.
How about this tactic for Trump getting a pardon:
It is “suddenly discovered” that President Trump needs to have surgery and be under general anesthesia. During that time, VP Pence is acting president. As acting president, Pence pardons Trump.
Does the VP get all the powers of the president if he has to be acting president in such an instance?
Hmm…sounds to me like there’s a pretty solid basis for a subpoena there. Trump can’t control Congress, much as he’d like to and would in a heartbeat if given the opportunity.
Depends on who’s on the Supreme Court when it gets to them.
Wait, what? Is a senior advisor to the President considered a “civil Officer of the United States”? More information, please.
Who would have standing to bring a case to the courts?
Any victim of the crime being pardoned. That could include the entire citizenry.
I don’t think it’s ever been tested, but I would be hard pressed to read “civil Officers of the United States” in Section IV as something other than the “Officers of the United States” in Section II minus military officers. Why do you think otherwise?
I simply don’t have any confidence that congress would subpoena or threaten Donnie half-scoop, or the son-in-law of Trump. They are gutless. They would respond by turtling. The system is screwed.
First off, I’m not sure the President has the power to pardon for contempt of Congress. Ex parte Grossman gives the President power to pardon criminal contempt of court, but as it points out:
In other words, the president can pardon contempt when it’s punitive, but not when it’s to compelling civil action.
Additionally, Grossman points out the simple fact,
Do you think Congress is just going to sit there and let the President impede their investigation? If he starts issuing pardons and then pardons of contempt and more on top of that, he’s killing himself politically, and just increasing the chances of his own impeachment.
We’ll let you be the test case for that. 
My fear is that the majority in congress (being the Republican members) would respond by quitting any investigations, refusing to discuss Russia anymore, and declaring victory.
Except that doesn’t seem to be what’s happening. Both Richard Burr, the chair of the Senate Intelligence Committee, and Chuck Grassley, the chair of the Senate Judiciary Committee, seem to be pretty committed to the Russia hearings, and I have to think that blatant interference by Trump will just get their backs up.
Section 3 of the 25th Amendment says:
There is no limitation; nothing in the text or the legislative history suggests that the powers and duties exercised by the Acting President are not those of the President.
Why would the guy whose doctor said he is in the best health of anyone in the history of the planet and aces all of his medical tests need surgery?
Here’s the scenario I see more realistically playing out. The Senate goes into recess and McConnell doesn’t leave it in pro forma session like he did with Obama. Then Don the Con fires Sessions and picks a new AG as a recess appointment, bypassing the Senate. This new AG fires Moeller, ending the investigation and no need for pardons.
Firing Muller would be a disaster for Trump. That’s not to say he won’t do it or try to do it, but the more it looks like he’s interfering with the investigation into Russian election meddling, the more suspicious it looks, and the more politically weak he gets.
I don’t think that matters to him. He wants to stay out of prison and doesn’t care how bad it looks. He’s got maybe 20% of the population that would fight over the chance to kiss his butt and a Republican majority who would overlook anything in order to play reverse Robin Hood. That 20% is not going to leave him no matter what, and they’ll primary any Republican that fails to show proper deference to their Dear Leader.
The President called his AG weak on twitter this morning. Other speculation is that Trump has asked Sessions to fire Mueller and Sessions refused, thus Trump is trying to insult him into resigning.
I wonder if a President has ever, in US history, openly insulted a member of his cabinet that he himself appointed.