Your $100M got you 4 years in Congress. Let's say you can pass a key bill that'll make you more than $100M. It had better not piss people off very much, because in the next election they'll buy TWO votes each and you'll have to spend $400M to keep your law in place. In the meantime, all those poor people you outvoted are $50,000 richer.
The interesting thing about this is that the more votes you buy, the more you fund your political enemies.
Being $X richer is now meaningless. Whoever is in power controls the currency and the time value of money sufficiently that they can manipulate the next round of voting.
The interesting thing about this is that the more votes you buy, the more you fund your political enemies.