It has started. In the dead of the night (1:05am on Thursday January 12th), the United States Senate voted to approve a budget reconciliation bill that would defund the Affordable Care Act (Obamacare) -- effectively killing that program. The vote was 51 to 48. All 51 votes to kill Obamacare came from Republicans. The 48 votes to keep Obamacare came from 45 Democrats, two Independents (King and Sanders), and one Republican (Paul). Feinstein did not vote.
Some had thought the Republicans would delay this, because they don't have anything to replace Obamacare -- and because there could be some serious political fallout from the 20 to 30 million people who will lose their health insurance without Obamacare. But they underestimated the sheer viciousness and stubbornness of the congressional Republicans. They hate Obamacare and they are going to kill it regardless of what happens to millions of Americans depending on it, or the political fallout from the repeal (evidently believing their own lies that most people want it repealed).
The bill must now be passed in the House of Representatives and then signed by Donald Trump (after he's sworn in), but there is little doubt that either will happen. The bill should have an easier time being passed in the House than it had in the Senate, and Trump has bragged many times about how he would sign an Obamacare repeal.
The Republicans are still promising to replace Obamacare with "something better", but they have been promising to offer a better plans for years now and haven't even come close to designing one they can agree on -- or one that will save the insurance for the 20 to 30 million people that were able to buy insurance under Obamacare (and will lose it when it's repealed).
This is a disaster in the making. Unfortunately, the Republicans don't seem to care. The only constituency they care about are the rich, and the rich are the only ones who won't be hurt by the death of Obamacare.