First chance they can, if they think they can get away with it.
Perhaps I'll regret saying this, but I don't think even the Democrats are that stupid.
Social Security was the "3rd rail" in politics for the longest time, and still is -- to a lesser extent. But, one of the reasons it's less "untouchable" is because so many people have alternative assets (401(k), IRA) to fall back on.
For most, Social Security doesn't have a "cash value" associated with it. Yes, you and I can assign a cash value to a future stream of income, but most people don't see it that way. So, adjustments to Social Security are only vaguely related to your pocketbook, unless you are already collecting benefits and see the amount reduced now.
However, even after the financial disaster of 2007 and 2008 (aided and abetted by the government, IHHO), account holders still have an accumulation of financial assets. It has a tangible value -- even if it's only a number on a monthly statement. It may be less than before, but it's still a real "nest egg", not just a promise of future income.
Any attempt by the government to grab that "egg" will be met with visceral reaction. Even if they tried to retroactively change the rules (i.e. making Roth IRAs withdrawals taxable), Congressional incumbents would become an endangered species.
I do expect them to modify the rules for future contributions -- i.e. reducing 401(k)/IRA contribution limits or even prohibiting contributions to Roth IRAs altogether.
With respect to the original article: my plan is to indeed convert IRA funds into a Roth IRA, but not now. I'm going to wait until I'm retired and living off non-IRA assets. My taxable income will be minimal, and my marginal rate will be much lower. You can continue to convert funds from an IRA to a Roth IRA until you are age 70-1/2, so there's no hurry.