The GOP ran furiously against Obamacare in the 2012 and 2016 elections. They attacked its perceived flaws from every possible angle, including from the left. They promised a new system that would cover more people and provide better coverage at a lower price. The nature of the new system, however, was never spelled out during the campaigns.
Once in power, Trump and the Republicans found they had no idea how to meet their conflicting promises, particularly since their hidden agenda was actually to make health insurance less, and not more, readily available. The Senate took a series of votes on a variety of different schemes, all of which would have made the public worse off than under Obamacare. All of them failed, because, in the final analysis, not enough senators were willing to vote for something that reduced the number of insured.
Sounds a bit like Brexit, no? Brexit was ridiculously oversold by its proponents, who are now offering a choice between becoming an EU vassal state or economic chaos. The correct answer is none of the above.