But let's look at the mandate. Yes, denying President Obama a political victory was obviously an important motivator, but it understates the extent to which Republicans have a genuine commitment to purpose that extends far beyond beating Democrats. And so it's actually no surprised that they aren't terribly fazed about accusations of cynicism when their imperatives require 180 degree strategic turns.
That's not intended as a criticism.
If you take public policy seriously, then it makes sense to maximize opportunities and minimize defeats irrespective of strategic or procedural consistency. When the goal was passing the Bush tax cuts, Republicans used the budget process in a controversial way to get the job done. When Democrats used the same process to round out health care reform, Republicans took a hard line against it. It's cynical politics. But if you believe in the Bush tax cuts and you want to stop health care reform, it's the right thing to do.
You can apply a similar test to the GOP's treatment of the individual mandate. The mandate arose as a conservative alternative to more liberal health care reforms like single payer and "Clintoncare." The goal was to have something fully baked and ready to serve up in the event that something farther reaching gained traction in Congress. Years later, when Democrats recognized that a mandate-based private insurance system was their best shot at achieving universal health care, Republicans abandoned it. On the surface it was schizophrenic, and suggested a certain nihilism about public policy. But apply a frame in which parties seek to maximize policy gains and minimize policy losses, and suddenly the GOP's actions make perfect sense. The conservative movement is heavily invested in limiting the size of the federal welfare state, particularly publicly run parts of it. A mandate was a perfect instrument for hedging against the risk of Medicare for All, or another single payer-like approach. But once that risk had disappeared so did the strategic value of the individual mandate. When Democrats embraced the mandate, restraining the growth of the safety net required Republicans to create a united front against it. So that's what they did. No apologies.
Whether or not three years on Republicans who once supported the idea have convinced themselves earnestly that their old views were wrongheaded is largely beside the point. As far as how politicians make and pursue policy goes, "motivated reasoning" doesn't provide a great deal of explanatory value.
N.B. In anticipation of some obvious counterexamples, obviously this model doesn't explain everything. But before you scream "Medicare Part D," consider that seeding public entitlements with private options -- and that's fundamentally what Medicare Part D is -- is consistent with the broader goal of unwinding the public safety net. Obviously there were other political considerations at the time. And debt-financing the expansion of an existing entitlement -- even with a private system -- put the GOP on the wrong side of some very powerful conservative advocates. It's hard to square that with an explanatory framework in which elected Republicans consistently try to limit the growth of the safety net. But the particulars of the Medicare Part D saga are unusual enough that I think it's fair to view that fight as an outlier.