How should Democratic candidates deal with January 6? It depends on the words and actions of the opposing candidate.
If the Republican clearly and openly expresses disdain for the rioters, there is no point in raising the issue. If he embraces the rioters, the issue should be front and center in the campaign, because liberal democracy itself will be on trial in the election. If, as in most cases, he equivocates in an effort to maintain party unity, he should be pushed hard until he makes a reasonably clear statement one way or another. That can be used against him with either the Reactionaries or the PBPs.
In my opinion, the best way to deal with the third group is to say that the public is entitled to believe the candidate supports the rioters unless he says otherwise. Or, in other words, silence means consent.