John Edwards was charged and acquitted on similar facts.
Note, though, that Cohen isn't being charged with unduly influencing the election. As far as campaign-finance laws are concerned, there's nothing wrong with influencing an election by paying hush money to a candidate's side piece.
Instead, the law simply asks that you disclose the money you spend when you file your campaign finance reports, and it prohibits direct corporate contributions to a campaign, as well as individual contributions in excess of $2,700.
Cohen went wrong by coordinating his work with "Individual-1" to help his campaign by providing valuable legal services and paying hush money to "Woman-1" and "Woman-2" without the campaign paying for it and without the campaign disclosing it.
Had Cohen been on the campaign's payroll, and had the hush money come out of the campaign treasury, and had the campaign disclosed it all on their campaign-finance reports, I think he would not be in any legal trouble (although there is the tax evasion, too).
I think it's probably safe to say that campaigns make these types of payments to people with damaging information somewhat frequently, and they don't get in trouble because the money comes from campaign funds (why would you want to go out of pocket, anyway?) and they report the expenditures as required. Because the campaign-finance laws are so loose, "disclosing" the expenditure isn't going to give anything away, because you can basically just say "$100,000 to Stephanie Clifford for personal services."