Today’s young Americans are the most likely of any generation to identify themselves as liberals. But their political enthusiasm for President Barack Obama and the Democrats appears to be waning.

That’s one finding in a wide-ranging Pew Research Center poll of so-called “Millennials,” the 18 to 29 year olds now making the passage into adulthood.

Young voters overwhemlingly supported Obama in 2008 in hopes that he would change the way Washington works. But more than a year into the Obama presidency, their political enthusiasm has cooled with the realization that Washington is still the same. Three in 10 blame Obama for the failure, while more than half say the president’s opponents and special interests are responsible.

That could help explain why the White House has quietly begun laying the groundwork for Obama’s 2012 reelection campaign, even as offiicials tell Politico that the main focus is the “gathering storm” of the 2010 elections.

As for young America’s characteristics beyond politics, Pew says the 50 million teens and 20-somethings are more racially diverse than older adults, less religious, better educated, more hopeful and almost physically connected to the digital world via cell phones and social networking Web sites.