Making her a martyr and firing up the D's is bad strategy. Being magnanimous will actually go a long way to keeping the D's in check while doing the important work that needs to get done.
I would have to disagree with the martyr concern. Most democrats know she is a crook. She was uninspiring as a candidate. I don't see how she would ever become a martyr. I think I see a much greater chance of Obama being seen that way by some people than Clinton. That is the main reason I would advise leaving him alone unless something major is uncovered.
1. Stepping back, what more would Democrats do in the name of a martyr that they are not already doing? Riot in the streets? Illegal voting? The democrats who might see her that way are already dead set against Republicans, Trump, and anything associated with them. The rednecks with guns are generally Trump supporters.
2. I think the Democrats in the media and Congress are going to oppose anything Trump does whether Hillary is around or not. Nothing changes.
3. The process to prosecute Hillary is something that would take months/years. If President Trump appoints a special prosecutor, he can go about his business and let that person lead the fight.
4. Trump's supporters expect him to prosecute criminals in D.C. and clean up out the corruption. They expect Hillary to be prosecuted. Pardoning known criminals is the path to failure. He already made the comment about seeing her in jail in the debate.
As a side note, I think people get too caught up with martyr concerns in general. It seems to come up all the time with killing terrorists and stuff. I think it is usually not near as big a concern as people make it out to be. It always seemed to be used as an excuse to do nothing. I never liked it.