Putting your mistress on the payroll and flying her around at taxpayer expense is more than just seeking female companionship. It should be a crime.
It’s probably the other way around, ie he began a relationship with his staffer, rather than making a previous mistress a staffer.
If it’s the latter and that can be proven, that might be an effective issue. Calling him adulterous scum for cheating on a wife that doesn’t remember him anymore won’t help though, at least I don’t think so.