Chief Justice John Roberts made the wrong decision about Obamacare, in my opinion. However, either intentionally or inadvertently, he has backed President Obama into a corner from which it will be much harder for him to be re-elected.
First, by siding with the liberal wing of the court, he has obliterated the "conservative judicial activism" argument liberals were waiting to use to explain the overturn of Obamacare. This also destroys the argument that Obama needs to be re-elected to be in a position to appoint "unbiased" (liberal) justices to the court in the future.
Second, by declaring the mandate to purchase insurance and the penalty for not purchasing it a tax, he has highlighted that all of the previous statements by Obama and liberal lawmakers to the contrary are completely false. These statements will be contrasted with the tax increases included in Obamacare and played over and over again until election day.
Last, he has made clear that the only option remaining to get rid of Obamacare is to replace Obama and lawmakers who voted for this unpopular law, then repeal it.