Another prominent voice is calling for a national conversation on expanding legalized sports betting outside of Nevada.

Sen. John McCain (R-Ariz.), speaking on "Capital Games" with ESPN's Andy Katz and ABC's Rick Klein, said Congress needs to hold hearings to discuss legalizing sports betting.

"We need a debate in Congress," McCain said. "We need to have a talk with the American people, and we need to probably have hearings in Congress on the whole issue so we can build consensus."

The Professional and Amateur Sports Protection Act of 1992 prohibits state-sponsored sports betting in all but four states. Nevada is the only state that allows single-game sports wagering. Delaware, Montana and Oregon have limited forms of sports betting.

When asked why Nevada should be allowed to offer sports betting, but no other state, McCain replied, "I think you've got an excellent point, and that's why it's an excellent issue."

McCain acknowledged that huge amounts of money are being gambled on sporting events, especially football. According to revenue numbers released Friday by Nevada Gaming Control, $3.9 billion was wagered on sports in 2014 at the state's sports books. But gaming experts believe that's only a small fraction of the amount that's bet illegally on sports in the U.S. The American Gaming Association estimates $138.9 billion was wagered illegally on sports in 2013. Some estimates have gone as high as $400 billion.

Estimated money placed on illegal sports bets dwarfs that of legal bets, according to the American Gaming Association. American Gaming Association

"I think that there [are] places for sports gambling in states, where gambling is legal," McCain said. "We obviously know that there are huge amounts gambled on sporting events, particularly football."

McCain's comments come nearly three months after NBA commissioner Adam Silver penned an op-ed in the New York Times in which he called for Congress to consider creating a federal framework to closely monitor sports betting and allow states to authorize betting on professional sports.

"I believe that sports betting should be brought out of the underground and into the sunlight where it can be appropriately monitored and regulated," Silver concluded.

New Jersey has been fighting to bring Las Vegas-style sports betting to its racetracks and casinos for three years. The NCAA, NFL, NBA, NHL and Major League Baseball have sued and successfully stopped New Jersey's efforts to this point. That case is headed to the Third Circuit Court of Appeals in the spring.