If the Supreme Court strikes down the mandate …
1) Listen to no spin, a striking of the mandate will deliver a mighty blow to the Obama administration. The Supreme Court may have lost some of its prestige, but enough remains that a negative verdict will wound. If nothing else, a declaration that the Obama administration's headline initiative is unconstitutional would go far to confirm the line of attack that Barack Obama is an alien who does not appreciate American ways and a revolutionist bent on overthrowing those ways.
2) A striking down of the mandate would not only attack the economic logic of Obamacare, but also blow up the political deal the administration reached with the insurance companies: more regulation in return for more customers.
3) For Republicans, a ruling of unconstitutionality would validate a central criticism of the law—and also conveniently avoid the need to offer more specific criticisms that might remind some voters of features of the law they might like, if they heard of them. The Republican slogan, "repeal and replace" has always bumped up against the problem that Republicans have no replacement in mind. If the Supreme Court dispatches the mandate for them, the Republican political problem dwindles away: with a victory in their pocket, they can take their time over producing a Plan B.
4) For lawyers, the striking down of the mandate will end a chapter in legal history: the era in which conservatives championed judicial restraint. From the 1950s to the 1970s, conservatives bitterly complained that liberals won in the courts what they could not win at the ballot box. Now we are returning to an earlier era, where conservatives looked to the courts as their ultimate ally—and it was liberals who seethed against judicial tyranny. The next Republican president had best prepare for a bitter Senate fight over his Supreme Court nominees.