"There are a lot of people who are racist," Reiner said on MSNBC's "Morning Joe" when asked to explain the millions of people who like what Trump says.
"Oh my God, did you just say that?" interjected co-host Joe Scarborough, a former GOP congressman. 
"They're not all racists," Reiner continued. "There's racism in this country that has been submerged for a long, long time and all of a sudden there's a man ... he's unearthed a lot of it."
Reiner pointed to Trump earlier this year not offering a strong disavowal of the support from former Ku Klux Klan grand wizard David Duke, arguing Trump doesn't mind such support.
"Do you see any racist people at the Bernie rallies? Do you see any skinheads?" Reiner asked, referring to the Democratic presidential hopeful.
"They're not all racists, but there is a strain there," he added.