There is some degree of regime uncertainty whenever an administration changes; had Clinton been elected, insurers would have had to worry about a public option that would compete with their offerings on the exchanges. But they could have been pretty confident that the administration would keep the exchanges in place, with much the same rules, and perhaps more importantly, that the administration would be doing its best to keep insurers profitable enough to entice them to stay on the exchanges.

Repealing Obamacare on a time-delay, on the other hand, ratchets regime uncertainty up to “Defcon 1.” The exchanges have so far mostly been unprofitable for insurers (although with big rate hikes in many states, that may change this year). The companies have stayed in largely because they’re hoping that the exchanges will be profitable in the future. If you announce that the law creating those exchanges will sunset in three years, to be replaced by some unspecified new program, then the companies’ incentive to keep offering insurance vanishes, and the exchanges will probably completely collapse in 2018, with a replacement plan still years away.

This is a compelling argument that repeal and delay is apt to go awry. But supporters of Obamacare shouldn’t take too much comfort in that fact, because whether or not Republicans pass “repeal and delay,” insurers will be facing considerable regime uncertainty — at a time when the exchanges were already so fragile that it’s far from clear they can withstand another blow.