The timing is "tactful" or tactical? It's short ranged and short sighted thought - certainly dim in terms of the thought spectrum. Doesn't make much sense to unleash a harmful practice with little chance of defense when it could be used against you in the future. If you think there aren't a lot of people who have skeletons in the closet (transgressions that are in vogue today but pretty much accepted practice years ago), then you are more naive than I thought. McCarthyism wasn't necessarily a one hit wonder.
I'm all for cleaning up politics, and abuses anywhere for that matter, but there is a time and place for everything. This one has "wrong headed" written all over it. Not for philandering - if true. However, allegations are just that and should be treated as such; they aren't necessarily fact; they aren't necessarily true; and allegations should not be accepted as either.
The big issue, though, is timing. The allegations were never pursued when they should have been. First they should have been presented at the time to remove from office an unfit person - if he was guilty of anything; second, they should have been presented when the statute of limitations was in effect - not past date allegations used for character assassination.
The other part is simply politics, and turning the process slimier than it already is. This is meddling and tampering because it traps a party (locked by procedural matters) to a candidate. If one political camp withholds damning information (whether true or false), prevents the other party from properly vetting a candidate, and then pulls the ambush when it's too late; it goes from dirty politics to sabotage of the electoral system. Something like a criminal trial without discovery and other rules to keep the process from being a mockery to fairness.
I'd think we would want to clean up the electoral process - not subvert it and cause it to be more tamper prone.