Sen. Chris Murphy (D.. Conn.) said Friday that it was "not likely" that a hypothetical assault weapons ban would involve taking back weapons like AR-15s that are already owned by Americans.

New York Times reporter Nick Confessore, whose newspaper published a widely panned editorial partially blaming conservative Republicans for the Orlando massacre, asked Murphy on MSNBC's Morning Joe what could be done about the "problem" of AR-15-style rifles that have already been sold.

"There are as many as eight million of these AR-15-style weapons already in circulation," Confessore said. "Is there anything you can do about those weapons already sold? Is the cat already out of the bag on this problem, to some extent?"

"I think that's difficult," Murphy said. "I think if we were ever to get an assault weapons ban back on the books, it's not likely that we're going to take weapons that are already out in commercial circulation back. What we know is that even as you make small dents in the number of high-powered and illegal weapons that are on the streets, you get lower gun crimes, and we've seen that in Connecticut."

President Obama has called for a renewed assault weapons ban in the wake of the Orlando terrorist attack, the worst on U.S. soil since Sept. 11. Murphy conducted a 15-hour filibuster this week to urge the Senate to act on gun control legislation, which included a proposed law that would ban people on the terror watch list from purchasing weapons.