You can earn a million dollars a year being on the board of a few companies and doing some speaking engagements as a former president. They also get I believe 200k a year, for the rest of their lives. I'm not sure what amount of money it'd take to make me give up my ethics as the president but it'd definitely need to be at least double digit millions a year, probably in perpetuaty before I was even tempted.

Former presidents/politicians on general normally fall into easy money gigs for whoever they were kind to during their term(s). Goldman Sachs routinely gives six figure single event speaking fees to former and presidential hopefuls. Sometimes they don't even have to show up and give the speech... Bribery is just strait up legal in America and a lot of the time you don't even explicitly have to do anything for them. They're just happy if you don't rock the boat.