On Wednesday, we noted how hugely important the black vote is for Democrats in 2014, for a few reasons:

1) It turned out big for President Obama but doesn't vote nearly as much in midterm elections.

2) It's heavily Democratic.

3) The 2014 Senate map includes an inordinately high number of states where the black vote plays a big role.

As it turns out, you can say all three of those same things about another key demographic: Young voters.

Young people were Obama's best age group in 2012, voting for him 60-37, according to exit polls. They also turned out at a rate of 45 percent which, while lower than 2008, was still significantly higher than it was in the 1990s.

There is also -- and here's the kicker -- a big potential for dropoff among these groups in key 2014 Senate races. That's because the 2014 map includes lots of states where young voters turned out in high numbers in 2012. In fact, a new Census report shows that 11 of the 19 states with the highest youth vote turnout in 2012 are holding key 2014 Senate contests.

The below graphic shows how that looks on a map.

You'll notice that almost all of the darkest (highest youth turnout) states -- Colorado, Iowa, Louisiana, North Carolina, New Hampshire, etc. -- are holding key contests in 2014. And even potentially competitive states like Minnesota, Oregon, Mississippi and Virginia had high youth vote turnout two years ago.

Of the 30 states with the lowest turnout, meanwhile, there are only five key 2014 Senate contests: Montana, Kentucky, Alaska, Arkansas and West Virginia.

Now look at the similarities to 270towin.com's map of competitive 2014 contests (these are the tan ones):

Courtesy: 270towin.com
Courtesy: 270towin.com

Now, one reason that key 2014 contests had big youth turnout in 2012 is that they are in swing states, which presidential campaigns tend to focus on (almost exclusively). So it's no surprise that states like Iowa, North Carolina, Colorado, New Hampshire and Virginia had among the highest youth turnout.

The good news for Democrats is that they spent the 2008 and 2012 elections getting young voters to vote at high levels in a lot of these states, so there should be something of a built-in advantage. They've been there before, after all.

But needless to say, the higher your turnout in one election, the more room there is for a dropoff in the next one. A recent poll from Democratic pollster Stan Greenberg showed that the key elements of the Obama coalition -- including young voters and African Americans -- remain much less likely to vote than other groups in 2014.

The maps above show just how painful that could be for Democrats.