Campaign contribution limits, term-limits etc are red-herring solutions. They distract from the real problem. As long as there is 20, 30, 40 or >50% of the GDP concentrated in the beltway, the crooked-politicians, crony-capitalists and the money-changers that created them will always find a way to get their hands on that mountain of buying power. You can erect no barrier to effectively block greed.
Fiat money reverses financial gravity and eventually pulls all assets into the hands of the money-changers.
Metal money (chosen by the free market) restores natural financial gravity and eventually moves all assets (including commodity money) into the hands of the producers.
The producers/people will then find their political power restored.
Therefore the correct answer is elimination of the legal tender laws.
The wrong turn that lead to this mess was made in 1812 with lopsided laws that allowed banks to satisfy debts with paper and simultaneously allowed banks to demand payment of the debts they held in specie.
See Ron Paul and Louis Lehrman, The Case for Gold: