Romney has won 14 of 25 state-by-state votes that decide which Republican candidate takes on President Barack Obama in November, compared to eight wins for Rick Santorum and just two for former House speaker Newt Gingrich.
These victories have given Romney almost 40 percent of the 1,144 delegates needed to secure the nomination. He has 446 delegates, Santorum 199 and Gingrich 117, according to authoritative poll aggregator RealClearPolitics.
"Mathematically, Rick would have to win 75 percent of what remains," Graham, a senior Republican who serves on various Senate committees, told ABC's "This Week" program....