While Republican National Committee spokesman Sean Spicer said in a statement before Trump’s comments that Democrats “bury their head in the sand on how dangerous the world is,” Trump’s insinuations go much further than mainstream Republican leaders are usually willing to go.

A source who works closely with the Trump campaign, granted anonymity in order to speak freely to NBC News, said after Sunday’s attack that the party had asked the candidate to offer condolences and then to stay silent. Trump clearly chose a different approach.

Dan Senor, a Republican strategist who served in the George W. Bush administration, told CNBC’s John Harwood in an e-mail that Trump’s comments on Obama “should be [a] serious concern” to officials tasked with providing classified briefings to Trump.