Another Bad Day In Court For Obama?

It would certainly appear so. Especially when even Justice Sotomayor, an Obama appointee, told the administration their argument "isn't selling very well."  That's probably because the administration's position in opposing the Arizona immigration law is so indefensible   As John Hinderaker put it:

what is going on here is that [the] Obama administration doesn’t want to enforce the immigration laws that Congress has enacted. The essence of its position in the Arizona case is that the federal government has the right to decide not to enforce the law, and if it so decides, then no state has the power, under the Constitution, to do anything that would tend to enforce those federal laws. So if the Obama administration decides that it will gain political advantage by ignoring federal laws against illegal immigration, states like Arizona just have to take the consequences without complaining.

They can't fault the Solicitor General for struggling to make that argument.