I realize that this is a simplistic reading, but the percentage of those that were undecided has declined by about the percentage of people that agree with that monstrous bill. It’s also worth noting that the media did, per usual, as bad of a job as possible in educating people on the bill and the Democrats, per usual, did an equally bad job of arguing against the bill or providing any real coherent alternative. Them being corrupt and benefiting from the bill too might help to explain that. Many Americans get fed propaganda by interests that benefit from that bill. So, Americans aren’t really being given tons of information to make an informed decision on that bill, and despite all of that, it is still deeply unpopular.
One thing I would say about that bill; if people wanted to critique it, they might want to point out that while it does give lots of tax cuts, those cuts benefit a small percentage of the population, they benefit the rich and corporations, and they are accompanied by the largest tax increase in American history. If we had a party opposing the Republicans that was worth a damn, and if we had a good media that wasn’t almost entirely owned by interests that benefit from their cuts, this bill would be about as popular as cancer.