"With guaranteed insurance for people with pre-existing conditions but no subsidies or individual mandate, premiums could skyrocket. Or, more likely, insurers simply would exit the market.... The upshot would be canceled coverage with no other options for people buying in the ACA's marketplaces ... as well as those buying directly from insurers, where the same rules apply. Even if the GOP eliminates only the individual mandate -- while leaving other aspects of the ACA in place for a period of time -- this could happen very quickly. But there are ways to avoid this potential chaos."