Many of his Hispanic supporters want an amnesty regardless of what it does to other Americans. He also has a lot of supporters who expect an Obama administration to do something other than continue the last three decades of pandering to the rich. All Obama has to do to keep his Hispanic supporters is show he's done a little more than Bush et al did for them—which consisted of empty promises and sub-prime mortgages that blew up on them.
Obama in 2012 will be running either with the first popular vote or with an electoral college shaped more by recent Hispanic immigration reflected in the 2010 census. Even if Obama got an amnesty for all 12 million illegal aliens, they won't become eligible to vote fast enough to do him any good in 2012.
What might help Obama electorally in 2012:
Requirements for naturalization have been way too loose in recent decades. Further loosening requirements will create long term problems—but those problems won't be apparent until after Obama is out of office. Above all, we can count on Obama to do whatever he thinks will get him re-elected in 2012.