Washington (CNN)Donald Trump isn't ruling out requiring all Muslims living in the U.S. to register in a national database to protect the country against terrorism.
Trump, who also said this week that he would consider shutting down mosques, said in an interview with Yahoo News published Thursday that "we're going to have to look at a lot of things very closely" when asked about a national database for Muslims.
Trump has repeatedly suggested it would be "insane" to allow Syrian refugees into the U.S. for fear that terrorists could infiltrate their ranks and slammed President Barack Obama for his plans to resettle 10,000 Syrian refugees in the United States over the next year.
"I think he's a threat to our country. I mean he must have some kind of a thing going because, you know, when you see that he won't even call them by their name, attack after attack after attack," Trump said Wednesday on Boston's WRKO radio. "It's radical Islamic terrorism and he won't even acknowledge it -- it's like they're coming out of Denmark or something."
Trump added that Obama "doesn't have any clue" when it comes to defeating ISIS.
The Republican front-runner's attack on the president came after Obama had slammed Republicans' calls to stop admitting any Syrian refugees into the United States as "offensive," "political posturing" and a "potent recruitment tool" for ISIS.
"We are not well served when, in response to a terrorist attack, we descend into fear and panic," Obama said earlier on Wednesday. "We don't make good decisions if it's based on hysteria or an exaggeration of risks."
Trump also slammed Hillary Clinton for not labeling the terrorist threat the U.S. faces as "radical Islam."
But Trump went beyond knocking Clinton for the language she uses in discussing the threat of terrorism, suggesting she lacks the "strength or the stamina" to lead the country.
"She doesn't have the strength, she doesn't have the stamina," Trump said. "Hillary does not have the strength or the stamina to be president, and she doesn't have the ideas."
In a separate interview, Trump knocked ripped Democratic presidential candidate, Bernie Sanders, as a communist.
"I think he's a communist. I think he's actually a communist with a socialistic bent," Trump told Yahoo News. "Anybody that would say that the Paris attacks were caused by global warming, there's something missing."
Sanders calls himself a "democratic socialist" and has said that he believes the greatest threat facing the country is global warming, and he linked climate change to unrest in the Middle East in the last Democratic debate.