The biggest is that creating a legal requirement binding future Congresses to impose supermajority requirements on themselves to change tax law is likely unconstitutional. That means Cain's plans would either need to change the Senate rules directly, or the Constitution itself. In either case, he'd need a two-thirds vote in the Senate just to pass his 9-9-9 plan. And that's not gonna happen.
"Senate rules, ok; but one legislature cannot bind another," emails Charles Fried, a Harvard law professor who served as Solicitor General under Ronald Reagan.
Cain's staff did not respond to a request for comment by close of business on Monday.
Let's pretend this wasn't an obstacle, though. Cain also says he sees his 9-9-9 plan as a sort of gateway to an even more controversial plan with the anodyne name "Fair Tax." More on the Fair Tax here.
Taking Cain's comments at face value, he'd impose a super majority requirement that would make it much, much harder for himself to move the tax code in an even more conservative direction.
It's worth pointing out that Congressional Republicans, under persistent pressure from the conservative movement, have been pushing similar requirements ever since President Obama took office. Most famously, they spent months fighting to send a Constitutional Balanced Budget Amendment -- one that would've imposed a super majority requirement on Congress for tax increases -- off to the states for ratification. This in effect would write Grover Norquist's "Taxpayer Protection Pledge" into the Constitution, forcing lawmakers to steadily slash away at government programs until deficits fell to zero, against a backdrop of very low revenues. In other words, it would require a fairly swift rollback of Social Security, Medicare and other popular programs, which has been a key goal for the movement for decades.
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