Repealing Obamacare isn't hard, they know everything to do to get rid of it and now is the time. However, the system of replacing is up in the air.
The first question is what to do and how to distribute federal subsidies? Should it be age based or tax based?
The second point is the modification of Medicaid. There would most likely be less federal funding. The devil is in the details.
The main issue is that Obamacare is massive and has had time to sit and sink into society. The effects of Obamacare has allowed many poor Americans to have insurance of some kind at the cost of raised premiums of all the insurance outside the government due to the people going to Obamacare. Turning the 20 million people back to the privatized insurance companies could prove difficult a transition. But due to Trumps new found affinity for Obama, the solution could be much more Democratic than expected.



