Rick Santorum laughed off Mitt Romney's Wednesday campaign memo which said that in order to overtake the former Massachusetts governor, Santorum or Newt Gingrich needs to start netting an "impossible number of delegates."

"It's pretty sad when all you have is to do math instead of trying to go out there and win it on substance and win it on what Americans want to hear about," Santorum told CNN at a town hall in San Juan, Puerto Rico.

Despite his dismissal, Romney does have a commanding lead. Even though former Sen. Santorum (R-Pa.) won in Mississippi and Alabama Tuesday, with Romney finishing in third in both states, Romney ended up winning the most delegates in the day's contests, thanks in part to late results in Hawaii and American Samoa. Romney won at least 41 delegates, while Santorum won at least 35, according to the Associated Press. To date, Romney has 495 delegates while Santorum has 252, by the AP count. To win the GOP presidential nomination, a candidate needs 1,144.

Puerto Rico has 20 delegates up for grabs in Sunday's primary, and Santorum likely hurt his chances by saying that the commonwealth would need to adopt English if it wanted statehood, something not required by the U.S. Constitution.