In 2010 it was discussed in Congress. LINK
It had no traction, so it was dropped.
Hillary Clinton made an attempt at a form of Obamacare when Bill was prez. 10-12 years later, we got "Universal Healthcare" or gov't takeover of healthcare rammed down our throats.
401k's will be seized eventually. It may take 10 years, maybe less.
There are many ways to takeover 401k's. They could force people to contribute 25% into gov't bonds that pay nothing. This could be added to what the Fed buys. There are many games they could play.
They could take it from the "rich" first, but that won't be enough. Then lower the bar slowly over time until you are considered "rich" just for having a 401k. They will call you mean spirited for not "sharing" it with people on food stamps. They will completely ignore the fact that you worked hard for years to save this money.
They will sign the bill on a Friday after 5pm, and no one will report on it until Monday, so it will be too late to make a move.