"Let's face it: The United States is under attack right now by ISIS and ISIS copycats," Weld said. "They have a deep pool to pull from. There are over 3 million Muslims in the United States — maybe Mr. Trump will want to deport them all, but the better approach is to work with the community."

Weld, who served as U.S. attorney and then assistant attorney general in the DOJ's criminal justice division, suggested that the DOJ could take a cue from a program that worked in Massachusetts. The "Drop-a-Dime Project," a nonprofit tip line created by community leaders, was used by law enforcement to pursue tips about crime in Boston's black neighborhoods and to achieve breakthroughs in drug investigations.

"We'd get all kinds of tips," Weld said. "The residents of Dorchester and Mattapan were only too happy to help. There may be some people out there leaning toward ISIS, people who would want to shelter the people going around killing other people. But for every pair of ears that would be sympathetic, there will be pairs that will not be sympathetic."

When he reentered politics this year to seek the Libertarian nomination, Weld spent the better part of two weeks assuring activists that he no longer favored new measures to restrict access to guns. Other libertarians went further, with the pro-gun gay group Pink Pistols arguing that "just as one might have a designated driver who stays sober, one might have a designated carrier with a concealed-carry permit who goes armed and does not drink." Tom Palmer, a gay libertarian thinker based in D.C., wrote today that "gun control advocates disarmed the victims at that night club."