Democratic presidential candidate Martin O'Malley on Friday lashed out at GOP front-runner Donald TrumpDonald John TrumpHouse Democrat slams Donald Trump Jr. for ‘serious case of amnesia’ after testimony Skier Lindsey Vonn: I don’t want to represent Trump at Olympics Poll: 4 in 10 Republicans think senior Trump advisers had improper dealings with Russia MORE's plan to place Muslims in a registry. 

"I have found that in times of crisis it's very important for leaders to remind us of the principles that we share as a people, the values we have as a people," the former Maryland governor said on MSNBC's "Morning Joe." 
 
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"When you hear people like Donald Trump talking about wanting to do ID cards based on religion. What the hell is that? I mean, how is that at all American?" O'Malley asked. 
 
Trump doubled down when asked by NBC News on Thursday night about a plan to establish a database to track Muslims. In another interview, he refused to rule out establishing a database and special ID cards for Muslims. 
 
Trump has floated the idea, along with closing some mosques in the U.S., amid stoked fears of international terrorism and debate over allowing thousands of refugees from Syria, a majority-Muslim country, into the U.S. over the next year. 
 
"We've got to put the brakes on the fear and politics of pander," O'Malley said Friday. 
 
O'Malley is one of three Democratic presidential candidates but has been polling in single digits, well behind Hillary Clinton and Sen. Bernie Sanders (I-Vt.). 
 
During the MSNBC interview, O'Malley also weighed in on Clinton's speech Thursday on combatting the Islamic State in Iraq and Syria (ISIS) after last week's attacks in Paris. 
 
O'Malley suggested that Clinton "leapfrogged" over the need for human intelligence on the ground regarding what happens after military intervention. 
 
"Secretary Clinton has had a lot of experience as secretary of State, but she hasn't shown an ability to really anticipate what comes next," he said.