Texas gained two congressional seats after the 2000 census, but Democrats and Republicans in Austin couldn't agree on a map, sending it to the courts to draw something fair. When Republicans took over both chambers in Austin in 2002, Tom DeLay saw an opening, and convinced the Texas state legislature to redraw the map mid-decade to screw over as many Democrats as possible. Five incumbent Democrats lost in 2004, while a sixth (Ralph Hall) switched parties. The map also served to protect every Republican incumbent except for one -- Tom DeLay. And we know what happened there.
You can see the map via this link.
Now, two years ago in Vieth v Jubelirer, the Court had four votes (Rehnquist, O'Connor, Scalia and Thomas) stating that poltically-based gerrymandering was never unconstitutional (or, rather, that there were no standards that the Court was competent to apply in determining when it had taken place), four votes (Stevens, Ginsburg, Breyer and Souter) for trying to find some workable standard, and Justice Kennedy in the middle, determining that he could find no workable standard to adjudicate this case, but holding out the possibility that some future partisan gerrymander might be so bad as to force the Court to come up with something.
So, what happened today? Here's a PDF of the Court's opinion. A majority of the Court determined that nothing in the Constitution prevented Texas (and, thus, every other state) from disrupting the stability of decennial redistricting and redrawing the map whenever it felt like, and rejected plaintiffs' contention that a mid-decade redistricting was sufficiently suspect on its own to determine that a redistricting was unconstitutional. The Court further declined to determine whether there was a general test to apply in the future.
However, partisanship was not the sole issue. The Court determined that new District 23, designed to protect weak Republican incumbent Henry Bonilla by making his district more Anglo-friendly, violated the Voting Rights Act by unlawfully diluting the voting rights of Latinos who remain in the district. Basically (and this is a complicated area of law), Latinos in the old District 23 were large and compact enough to constitute a majority of a district, but weren't any longer. Said the Court:
District 23's Latino voters were poised to elect their candidate of choice. They were becoming more politically active, with a marked and continuous rise in Spanish-surnamed voter registration. . . . In successive elections Latinos were voting against Bonilla in greater numbers, and in 2002 they almost ousted him. Webb County in particular, with a 94% Latino population, spurred the incumbent's near defeat with dramatically increased turnout in 2002.  In response to the growing participation that threatened Bonilla's incumbency, the State divided the cohesive Latino community in Webb County, moving about 100,000 Latinos to District 28, which was already a Latino opportunity district, and leaving the rest in a district where they now have little hope of electing their candidate of choice. . . .
Against this background, the Latinos' diminishing electoral support for Bonilla indicates their belief he was "unresponsive to the particularized needs of the members of the minority group." Ibid. (same). In essence the State took away the Latinos' opportunity because Latinos were about to exercise it. This bears the mark of intentional discrimination that could give rise to an equal protection violation. . . . The State not only made fruitless the Latinos' mobilization efforts but also acted against those Latinos who were becoming most politically active, dividing them with a district line through the middle of Laredo.
These are the basics, so far as I can tell. Bonilla's district will have to be redrawn, and who knows how many other districts will be affected. (I'm also not sure when this will take place; presumably, not in time for November.) The Court's opinion is a mess, and this is going to take a good amount of sifting. Thank goodness I'm not the only lawyer here.