The Bush administration spent five years and purged its own attorneys trying to dig up some cases of voter fraud they could prosecute. In that time, they convicted a grand total of 26 people. If there was the slightest evidence that 'thousands' of fraudulent votes were being cast, it would have emerged by now.
We're essentially talking about hispanics voting illegally. Bush and Rove seriously believed they could turn hispanics to vote Republican in significant numbers, hence the "ownership society" and all that. They never had any strategic interest in anti-immigrant actions.
