Pew Research reports:
Trends in the opinions of America's youngest voters are often a barometer of shifting political winds. And that appears to be the case in 2008. The current generation of young voters, who came of age during the George W. Bush years, is leading the way in giving the Democrats a wide advantage in party identification, just as the previous generation of young people who grew up in the Reagan years -- Generation X -- fueled the Republican surge of the mid-1990's.
In surveys conducted between October 2007 and March 2008, 58% of voters under age 30 identified or leaned toward the Democratic Party, compared with 33% who identified or leaned toward the GOP. The Democratic Party's current lead in party identification among young voters has more than doubled since the 2004 campaign, from 11 points to 25 points.
In fact, the Democrats' advantage among the young is now so broad-based that younger men as well as younger women favor the Democrats over the GOP -- making their age category the only one in the electorate in which men are significantly more inclined to self-identify as Democrats rather than as Republicans.
Ezra Klein notes:
Political scientists argue that the more often someone votes for a party, the more that preference gets locked in. Each vote marginally increases your personal identification with the party you pulled the lever for. Three election cycles, and you're probably a partisan for life, or something near to it. Which means an advantage like this, though potentially temporary, also opens the door to a more enduring electoral edge with this generation.