* The typical bribe is, you do something in your role as a government official, and later you legally get a high-paying job, or they pay you $100K-$200K/hour in speaking fees (the low number is Bush Jr's and the high number is Hillary's, AFAIK), etc. Works great with legal electronic payments.
* "Buying votes" usually means, either you promise government money to a group of voters, or you promise a donor to do something when you get elected. Either way, you're buying votes with the government's money so no need for cash. If by buying votes you mean that you're Trump and you're paying for your campaign, again, nothing illegal there, I doubt he travels with stacks of cash.
* "Hookers/strippers"... I dunno, whatever the problem with electronic payments there... I think a politician is in the best position to find a workaround, certainly in a better position than the average customer. In particular, if the workaround involves getting someone else to pay for it electronically, a politician is in a great position to reward that someone.