I want to start off by saying that I don't support Donald Trump or the GOP at all and don't know Billy Walters personally. In fact I think Donald Trump is probably guilty of crimes that would warrant impeachment or worse. And I think Walters is probably guilty as well; even knowing the FBI and Davis lied in the case, the evidence against him still seems strong, and his sentence did not seem excessive when compared to similar recent sentences for the same crime. All this aside, strategically, a Billy Walters pardon is an amazing opportunity for Donald Trump in his current situation.
For a pardon to make sense, there usually have to be several boxes checked. First, there typically has to have been some injustice done. And in the Walters case, the level of criminal misconduct on the part of the FBI was simply staggering. Grand jury testimony was leaked, the star witness lied to get a reduced sentence, and apparently - although this is just a claim by the defense - the key piece of evidence, the "bat phone", never even existed during the time period that the alleged illegal conduct took place, and the prosecution knew this yet lied all along. Even the FBI who typically does nothing against their own was forced to act by suspending one of the agents in the case. While I am not a lawyer I suspect that had Walters not been facing extremely strong evidence he would have been a huge favorite for a dismissal pre-trial or win on appeal. In short, Billy Walters was a victim of the exact same sort of misconduct that Trump claims he is facing on a daily basis. A pardon here would give him the chance to send the message to his supporters that he is going to do whatever it takes to shut down this sort of misconduct and clean up the FBI, even if he can't stop the Mueller "Witch Hunt" due to the RINOs and Democrats who are plotting against him.
Of course, Walters is not the only victim of these illegal tricks, as the FBI uses them to get convictions all the time, sometimes against defendants who are not even guilty. And the second box to check is that the pardon be politically favorable, and handed out to the "right" person. This is what really makes the Walters case a great choice for Trump. First is the crime itself, insider trading, hardly a heinous crime in the eyes of most. While most everyday people understand insider trading is illegal because of the Martha Stewart conviction, they usually don't understand the reasons why, and many who understand don't care anyway. For example, Phil Mickelson, who was just as guilty as Walters but got off on a technicality, does not seem to have suffered any loss of popularity as a result of his involvement in the scheme, and instead is off to play Tiger in a couple months for huge PPV money.
Another thing that works in favor of a pardon here is that this was an extremely high profile case, headed by Preet Bharara, a well-known Democratic Comey-supporting Obama appointee. The idea, of course, is that these are the same "17 Obama Democrats" that are investigating Trump now. It seems like wiping out one of Preet's big wins would be a great opportunity to stick it to the "libs" and show them who is boss.
Finally, the last box to check is that the pardon be given to a sympathetic figure. Walters is a lifelong Republican donor which certainly works in his favor, although I don't know if he supported the Trump campaign. He is also well-known for his generous support of charitable causes. But unlike most rich big donors, having won his money through gambling Walters is more of a Robin Hood story, and nowadays most people would probably tend to give a sports bettor more respect than your typical greedy CEO. In other words, it would not look like Trump was bailing out one of his rich criminal cronies, helping him in the court of public opinion.
The pardon would not have to come for free. It could be given with the expectation that Walters would go on a media campaign suggesting that Trump is a great man who is currently the victim of the same sort of FBI lies that he has had to battle his entire life. I can see a lot of people buying it. And with sports betting exploding and Walters being a legendary figure in this area, even with the liberal media it is likely there would be no shortage of opportunities in the media to press this case. Trump could gain an ally, drum up some additional public support, and stick it to one of his personal enemies at the same time. While it may not make much difference, at this stage he needs to do everything he can.