“I would certainly implement that,” Trump said Thursday, according to MSNBC
Asked whether Muslims would be legally required to sign up for such a database, the businessman said, “They have to be. They have to be.” 
“[The database] would stop people from coming in illegally. We have to stop people from coming into our country illegally,” he added.
When asked how his plan differed from prewar Nazi Germany, Trump repeatedly responded, "You tell me."
Trump had said earlier Wednesday that he believes that the war on terror will require unprecedented surveillance of America’s Muslims.
“Certain things will be done that we never thought would happen in this country in terms of information and learning about the enemy,” he said in a Yahoo interview. “We’re going to have to do things that were frankly unthinkable a year ago.”
Trump, who rose to the top of the GOP presidential race by focusing on immigration, has repeatedly opposed President Obama’s push to bring 10,000 Syrian refugees into the U.S.
He warned Wednesday of a possible “Trojan horse” in the form of terrorists posing as refugees to get into America.