Basically the DOJ is refusing to defend Obamacare in Court, on the grounds that they think it's unconstitutional. This is not good, and I say this as someone who is not a fan of the ACA by any stretch.
This is bad bad bad bad.
Think about immigration from this perspective
If DOJ won't defend a statute when the government is a defendant - no one else really has standing to do it
Courts could get in the habit of appointing amici (friends of the court), but that's unwieldy