Voters under 30 – the so-called millennial generation – propelled Barack Obama to victory in 2008, voting Democratic by a historic 34-point margin, which separated  it from older generations of voters by a wider gap than ever before.

That preference gap persists, a new Pew Research Center study finds, with younger voters still backing the president by much greater margins than older generations.

But will millenials participate in the next election with a commensurate level of engagement, turning out for Obama in 2012?  Pew found their  enthusiasm substantially waning: Only 49 percent approve of Obama’s job performance.

Moreover, only 13 percent say they have given a lot of thought to the presidential candidates compared with 28 percent four years ago; and only 17 percent say they are following election news  closely, down from 24 percent.

“They are a lot more disappointed with Obama, and their enthusiasm, their interest in voting, their interest in politics is way down,” says Pew associate director Carroll Doherty. “There’s a year to go and a lot can happen, and there’s no opponent for Obama yet, or Democratic primary to get voters engaged. But this enthusiasm gap has got to be worrisome for Democrats, because this was Obama’s strongest age group in 2008.” 

 Meanwhile, silent generation voters (born between 1925-1945), baby boomers (born between 1946-1964) and the generation Xers who came after the boomers, are all showing higher campaign interest and engagement now than they did in 2008.  They’re also much more likely to favor Republican candidates, Pew found.

In Pew’s  hypothetical match-up, for example, gen Xers, boomers and silent generation voters all favor Romney over Obama. Only millenials say they’ prefer Obama.

“When the primary season starts to wrap up, look for where the younger voters are at that point, and then where they are over the summer in terms of their own interest and engagement in this election. If you still see them lagging behind 2009, then that’s a very bad sign for Democrats,” Doherty says.

Pew’s findings come from two major national surveys conducted between Sept. 1-15 and Sept. 22-Oct. 4, comprising a combined 4,413 adults.  They were supplemented with Census Bureau data. The margin of error for generational groups ranges between 4 and 6.5 percentage points.