From this article:
There’s a reason Republicans have been rushing to try and defund the Affordable Care Act before October 1, when major sections of the law take effect.
Once state health insurance exchanges take effect, and premiums for all Americans go down, Republicans know the law will only become more popular and harder to repeal.
As Republican Senate Minority Leader Mitch McConnell said, “It’s a lot harder to undo something than it is to stop it in the first place.”
Because just like Republicans railed against Social Security and Medicaid and Medicare when they were first proposed, those programs are now highly effective and broadly popular parts of our social safety net — supported even by strong majorities of Republican voters.