Why attack him and give rise to a martyr syndrome?
Let the cause die in silence by ignoring it.
He did it. Can you PROVE he did it to a jury that includes his supporters?
IF you do not convict, then he has a ton more press and can further bring news to his cause, and you make HIM the victim.
They've already got a martyr complex going strong. That's why they believe the election was stolen.
As I see it, not pursuing him for his myriad crimes is tantamount to conceding that they were not, in fact, crimes. In addition to then allowing him and his cultists to scream victory and dismiss the allegations entirely, it also sets a precedent for future presidents. When President Hunter Biden/Hillary Clinton does whatever and argues they are being discriminated against by the DOJ, they'll be entirely right to say so. And if Trump regains the presidency, well, that means he can do just as much again with impunity.
Nor is this unique to Trump. At the very least, GWB and his cronies should have faced justice, too (though of course the same is true for many of their predecessors, too). But they didn't, and now it's really hard to roll the tape back on torture (as Obama discovered), pre-emptive war (the Iran sabres will start to rattle again very soon), an out-of-control national security state, etc.