If Matt Gaetz were Trump, then he would most-probably be committing an impeachable act, because the intent of the pardon would be to obstruct justice. (A president does have full power to pardon anyone for any reason, but it can't be done with illegal motives. Keep in mind that Rod Blagoevich as Illinois governor had every right to name a Senate replacement for Barack Obama, but when he attempted to illegally sell that seat, he went to prison.)
Matt Gaetz would also be stupid because Manafort could and will still be prosecuted for state crimes, so the pardon would be pointless - while getting you impeached.
That's the thing to keep in mind with all these pardons. Robert Mueller is not a stupid person. He's known full-well, from the very beginning, that Trump might try to pardon anyone who pleads guilty or gets convicted. So, from the very beginning, Mueller has been working with several state Attorneys General, and state crimes have been an important part of the process. And a presidential pardon does not cover state crimes.
This holds true for Trump himself. Any talk of Mike Pence pardoning Trump, if Pence ever became president, misses the point that we already know of cases being built against Trump -- and his company and children -- for state crimes having to do with the Trump Organization and Trump Foundation. And no presidential pardon will help anyone there.
Which is why all that a pardon by Trump will do is add one more brick to an impeachable charge of obstruction of justice.
All that said, I hope Trump doesn't pardon any of this low-lifes who have been working against America's interest with its strongest adversary. It's just that, if he does, he's still screwed.