"How many non-citizens participate in U.S. elections? More than 14 percent of non-citizens in both the 2008 and 2010 samples indicated that they were registered to vote. "
That's impossible, because noncitizens can't vote.
Well they can't legally vote, but since anyone can register my mail to vote, anyone can vote.
The Cooperative Congressional Election Study (CCES) found that actually non-citizens register to vote, as indicated above, and they do vote. Perhaps requiring valid photo IDs will reduce this fraud.