Yes, I've also read that concern (tax law changes negatively impacting 401ks/IRAs) more than a few times in the past decade. And it always seems to follow that an alternative to 401ks/IRAs are peddled as a 'better' retirement investment choice. Roths are especially targeted as being susceptible to a change in the tax code.

I see two issues with the attacks on 401ks/IRAs.
1) If (a very big IF) the tax code changed for 401ks/IRAs, current savings in those vehicles would almost certainly be grandfathered.
2) The GOP is very unlikely to support negative changes to 401ks/IRAs because their efforts are more aimed at Social Security. If Social Security programs are reduced through any of the popular proposed methods - chained CPI, raising retirement age, means testing - 401ks/IRAs become even more important for retirement planning and in my opinion less likely to be changed.

My biggest concern about retirement is the likelihood that Social Security benefits will change. I have much less problem with chained CPI and changes in retirement age than I do with means testing. The problem that I have with means testing SS is that it discourages saving for retirement - I consider that to be an unforgivable sin for governments. With pensions rapidly becoming a thing of the past for American workers, I think that government should increase incentives for Americans to save in both 401ks and IRAs.

As far as political reality, the GOP will control the House due to Congressional districting until the 2022 election. If current control of state legislatures remains, there will be even more Congressional districts gerrymandered in favor of the GOP after the next census. Going into the redistricting following the 2010 census, the GOP controlled 57 state legislative chambers; after the 2016 election, the GOP controls 66 state chambers. The same goes for gubernatorial elections - after the 2010 election, the GOP had 29 governorships; after the 2016 election, the GOP has 31 governorships.