He's gonna use the shit out of all of us....

Pardoning is basically the one presidential power that works the way Trump thought ALL of being president worked. He's gonna use the shit out of it.

— David Roberts (@drvox) May 31, 2018

I think Trump is testing the waters with his pardons, and his announced possible pardons.  He makes sure to pardon celebrities, not people no one has heard of.  He makes sure to do it himself, not through the Office of Pardons of the DOJ.  It is a Presidential power that is all but unfettered, and so he wields it to his heart's delight.  But he's also taking the temperature of the room.  The power to pardon is a political power.  It put a permanent asterix beside the name of Gerald Ford, the only President in U.S History to never have been elected to the office.  Ford sealed that fate the day he pardoned Richard Nixon.  G.H.W Bush learned from Ford's example, and pardoned the Iran-Contra defendants on his way out the door, a fitting capstone to his political career.  It saved Bush's posterior from criminal exposure in the matter, ended the special prosecutor's work, and cost Bush nothing as he ended his political career with his one-term in the highest office in the land.

And now Trump is throwing out pardons in a "scattershot" manner, except we've all heard of the people he's pardoned, or may pardon (Martha Stewart, Rod Blogojevich), and they all have (with the exception of Stewart, who knows Trump personally), some connection to bashing (or selling the Senate seat) of Barack Obama.

Celebrity; and bashing Barack Obama.  That's what Trump is up to; but he's testing his political strength, too. If he starts pardoning Michael Flynn or Paul Manafort, how will the public react?  Cohen, Flynn, Manafort; they are not celebrities.  If they don't turn on the President, the lesson is supposed to be, he will pardon them before they spend (well, too much, anyway) time in prison.  Except, of course, the legal system doesn't work that way.

In "Goodfellas" the protagonist goes to jail for the first time, but he doesn't talk.  He does his time, and returns to his fellow gangsters a hero because of his silence.  But that code of omertà is bought at the risk of death; in the end, when he does talk, he has to enter witness protection to stay alive.  Nobody is going to kill Cohen or Manafort if they turn on Trump; and if they don't?  They can still be compelled to testify.  If they are asked to testify about matters related to their conviction, the 5th Amendment no longer applies (double jeopardy protects them from further prosecution, except for perjury).  If they have been pardoned, they also no longer have 5th Amendment protection.  So what does Trump gain if he starts handing out pardons?  Not much, really, unless he's also willing to hand out pardons to obviate perjury proceedings (which would have to be a separate pardon, in each case). And at what point do those pardons become the problem themselves?  No, he can't be prosecuted for using the Presidential pardon power, and no, it doesn't really rest on showing use of that power has become obstruction of justice (imagine the opinions that case would generate at the Supreme Court).

But he can be impeached.  And once impeached, he can be prosecuted; and again, those pardons won't prevent his "friends" from being compelled to give testimony; and without a pardon power, he can't protect them from being charged with perjury.  And if the cases come up in state court, he's powerless anyway.

There is some speculation that Trump is sealing his fate in the Senate, where Jeff Sessions was a member much longer than he was the Attorney-General.  The argument points out that Senate members have lifetime privileges in the Senate, including access to the dining hall, the gym, and even the floor of the Senate.  It's a privileged club of 100, and that privilege lasts a lifetime, especially if you've served more than one term with Senators who have also served more than one term.  And the news about how Trump is treating Sessions is not going unnoticed.  No, Senators are not defending Sessions in public; but might they do it in an impeachment trial?  Why wouldn't even a GOP Senate replace Trump with Pence?  Especially if it turns out Trump won in 2016 because more of the electorate disliked the known quantity of Hillary Clinton than disliked the lesser known quantity of Donald Trump?  Did he really win the election, or did Clinton lose it?  And if Trump has no coat-tails in November, what do the Senators owe such a lame-duck?

What counts as obstruction of justice in a court of law is not the same thing as what counts as "bribery" or "other high crimes and misdemeanors" in an impeachment trial.  And an impeachment trial is not a criminal trial conducted by an independent judiciary zealously guarding its procedures of due process.  Remember Nixon resigned because the jurors of his trial told him the fix was in, even before the House had voted on articles of impeachment.  There is nothing to prevent a majority of Senators from reaching that conclusion again, long before a trial is begun.  If Trump stops bestowing pardons on celebrities because he can, and starts using them to do what he can't get Jeff Sessions to do, before or after November, Trump might get a similar visit before his first term is over.

And he's still trying to figure out if he can get away with it.  As he likes to say, "We'll see."