Details here and here: the short version is that the USSC decided that a lower court erred because it had, to quote the New York Times, "not paid enough deference to the Legislature’s choices and had improperly substituted its own values for those of elected officials." The underlying issue is that there is an ongoing dispute over how the new Texas federal Congressional map should be drawn; Texas got four more seats in the latest round of redistricting, and the beleaguered Democratic minority in Texas has been using Section 5 of the Voting Rights Act as their excuse to tie the entire process up in legalistic knots. As primaries are, well, looming at this point, the aforementioned lower court (in San Antonio) had put together an interim map that more or less ignored the elected legislature's wishes in this matter; and the Supreme Court just unanimously smacked them down for it.
This does not mean that the original Texas legislature's maps will be used; that's up to the currently Democratic-controlled Justice department, or else an ostensibly impartial three-judge tribunal in DC. What it does do is reaffirm the principle that lower courts should take into account the original wishes of the legislature in emergency situations - and with an effective deadline of February 1st, this qualifies as an emergency situation - such as these. In other words, the courts may still create interim maps (which will apply for at least the 2012 election cycle) while the final maps are being resolved; what they can not do is ignore the original wishes of the legislature, to the extent that the San Antonio court did.
At a guess, this ruling puts renewed pressure on the courts to resolve the remaining lawsuits over the original maps; as was mentioned before, there is a fairly serious deadline of February 1st (the primaries have already been pushed back to April). The 2012 Congressional elections must take place, and Texas is Constitutionally entitled to those four extra seats in the H0use. And if the existing maps are not cleared, there still remains a need to have something in place that takes into account Texas' increased representation; and that must be something that can be legitimately seen as taking into account the wishes of the duly-elected state legislature of Texas.
In other words, the clock is ticking.
Moe Lane (crosspost)