Really, striking down the ACA isn’t even testing the far reaches of the Court’s power. The Court would have substantial support in Congress and, at least as of now, would appear to have the support of the majority of the public. I wish it weren’t so, but I don’t think the Court would face any significant loss of public legitimacy should they strike down the ACA.

David Bernstein's view:

At most, a ruling against the ACA will have the same effect as Bush v. Gore or Citizens United, or Roe v. Wade and Boumediene for that matter; a fair amount of caterwauling, with the Court as an institution remaining unscathed.