Trump would use tariffs aggressively as an instrument of foreign policy, GATT be damned, I guess. Cruz would use a consumption tax: the best revenue method, but without the policy bite of tariffs. They would be a potent combination.
GATT ended 1995 with the creation of the WTO. The WTO agreements allow the imposition of tariffs for countries faced with chronic trade deficits, which we are. And I believe there is also a provision to deal with currency manipulators which could be used to target China specifically.
Tariffs are better than a consumption tax. Tariffs protect our industries. I’m not sure funding the government entirely by tariffs or consumption taxes is a good idea. Both are subject to the ups and downs of consumer psychology. Which means that during an economic downturn, government revenues fall off as well, making it harder for the government to use fiscal policy to do anything to soften the downturn. And it means debt grows more rapidly as safety net payments rise even as gov’t revenues fall.
The Income Tax is more stable.