So what happened with the youth vote in 2010?

Well, you can expect to see a lot of this in the coming days:

The youth vote was a bust for the Democratic Party this year. Young voters plummeted as a share of the electorate and support for the Democrats declined. Where young voters went for Obama by a two-to-one margin, barely more than half supported his party yesterday. Young voters made up just 11% of those casting ballots. Obamamania was a fad, and it’s over.

On the other hand…

Young voters were the only age cohort to support the Democratic party yesterday, and though their support for the Dems did decline, it declined less than any other age group’s. Between 2006 and 2010 over-65 voters’ support for the Dems dropped by nine points, 45-64 year olds’ dropped by seven, and 30-44 year olds’ dropped by six. But the proportion of young voters supporting the party dropped by just four points — from 60% to 56% — and their support for the GOP rose by just two points.

Young voters were the only age cohort to support the Democrats this cycle — as noted above, 56% of them cast their votes for that party. No other age group gave more than 47% of their votes to the Dems, and seniors went for the GOP by a 58-40 margin after narrowly supporting the Democrats in the 2006 elections.

Young voters’ turnout as a share of the national electorate stayed pretty much stable when compared with four years ago — the figures I’ve seen suggest that it dropped from 12% to 11%, but given the way the numbers are counted, that may just be statistical noise. (Also, I haven’t seen any national turnout numbers yet, but if voting was up across the board then the youth vote could have risen considerably while not showing any increase as a proportion of the whole. I’ll update when I get that data.)

Turnout is lower for midterm elections than it is in election years. That’s true for every demographic, but the dropoff is particularly steep for youth voters. That’s always been the case, and it likely always will be. Old people vote in the midterms and young people (including people in their thirties and forties) don’t. Also, youth support for Obama in 2008 was so intense that a regression toward the mean was inevitable.

So no, young voters didn’t save the Democratic party yesterday. (Given the way the party has treated them for the last two years, it would have been shocking if they had.) But yesterday could have been a lot worse for the Dems, and if young people had stayed home, or voted in line with the way that older voters did, it would have been.

Update | While I was working on this piece, the Washington Post put up a story on the youth vote that followed the script I warned about above pretty much to the letter. It’ll be the first of many.