Seems even less likely now with control of both houses than it was the last 2 election cycles. Like you, I see changing the tax brackets as the biggest risk. There could be some changes around the edges, but most of these politicians aren't going to vote against their own self interests. They all have family and friends that use these retirement vehicles. If they get voted out office, they will wan't the max limits at their new lobbying firm..
The governments desires to control all money and give it to who they want will destroy all savings. No, they won’t come and just take it away, first they will protect all retirement accounts by taking away your access to it and then guaranteeing a return of some percentage of it. They will make sure you get your 3% when the inflation rate is 15%.
Put your money in anything that cannot be grabbed by the government.