The core problem with ObamaCare has always been that its economic model is unsustainable. You can't mandate guarnateed coverage to those who are elderly or already sick without allowing insurers to charge what they'll need to cover the costs of such benefits. The Obama Administration tried to do it by mandating that everyone buy health insurance in order to expand the risk pool, but that requirement was ineffective and wildly unpopular - and now it's gone as part of the tax reform bill passed at the end of last year.
Because the Democrats knew they were mandating a system that couldn't stand up under its own insane structure, they built into ObamaCare a mechanism to bailout health insurers who lost money complying with the law's coverage mandate. When Donald Trump ran for president, he railed against these bailouts, rightly calling them one of ObamaCare's worst hidden elements.