The only way to actually ensure that no millionaire, anywhere, pays less than 20% on their annual income would be to essentially suspend the rule of law for wealthy people, and give the IRS power to seize income from rich people at will within some very broad guideline about fair shares.
What’s Wrong With the Buffett Rule? - Megan McArdle - Business - The Atlantic
Apparently Megan McArdle has a very poor imagination. There is nothing conceptually complex about a minimum tax rate that kicks in at certain levels of income. Without exceptions or deductions it would be undesirable, but it certainly wouldn’t erode the rule of law or require any kind of executive discretion.
