Sanders had expressed concern about North Korea during last week's debate.
Trump has previously sparked outrage by retweeting user "WhiteGenocideTM."
Trump celebrated his win in New Hampshire by hammering the competition in South Carolina.
Rubio questioned Trump's temperament and said Bush "has no foreign policy experience."
"I’m not just going to walk away from the millions of people supporting me."
He went after Cruz for telling Carson supporters their candidate was quitting.
"I don't think there's any doubt," said the former White House press secretary.
Julian Hattem 02/10/16 04:19 PM EST
The emails reportedly hit the inboxes of many of Clinton's top aides.
"Bernie Sanders has been largely missing in action," Rep. Hakeem Jeffries said.
Right to Rise USA has now invested more than $10 million in the Palmetto State.