On Tuesday, a district court panel threw out Virginia's map of Congressional districts, finding that one district was unconstitutionally racially gerrymandered in violation of the Equal Protection Clause. "Individuals in the Third Congressional District whose constitutional rights have been injured by improper racial gerrymandering have suffered significant harm," a two-judge majority of the panel wrote.

Virginia has 11 Congressional districts. In 2012, Republican House candidates won 51 percent of the votes cast in the state — and they ended up winning eight seats, to the Democrats' three. Here's what the partisan results looked like:

All three Democrats won with more than 61 percent of the vote, but most Republicans won with margins in the mid-fifties — a classic sign of gerrymandering, indicating that the Democratic-leaning voters were packed into a small number of districts. But the US Constitution doesn't prohibit partisan gerrymandering, so that won't lead a court to toss out the maps.

Democrats argued that black voters were being unconstitutionally packed into one district to dilute their voting strength

Partisanship in the US, though, is often intertwined with race. If you look at all the blue in the southeast of the state, that's just one, heavily-black district — the third, represented by Bobby Scott (D). In fact, it's the only majority-black district in the state — even though about one in five residents are black.

So when state Republicans proposed this map in 2011, Democrats argued that another majority-minority district should have been created, and that black voters were being unconstitutionally packed into the third district to dilute their voting strength. Though the GOP got the map through the narrowly-divided state Senate by just one vote the following year, Democrats soon sued. Now, a majority of this district judge panel has agreed with their criticism.

The district court has ordered Virginia's legislature to pass a new map by April 1, 2015. The GOP legislature would still draw up the new maps, which could limit hopes of Democratic gains. But the Republican governor who signed the original maps, Bob McDonnell, is no longer in office (and is currently awaiting sentencing after being convicted on corruption charges). Now, the new Democratic governor, Terry McAuliffe, can veto any new map.