"I've actually called him up and said, 'Donald, listen, you need to speak in complete sentences at debates," Scarborough said. "After the second debate ... I walked into his office, I said, 'Donald, do you know how to read? ... I said, 'You should read before a debate! ... Read a paragraph on Syria, read a paragraph on education reform!'"

The anecdotes, which were meant as a testament to Trump's off-the-cuff political savvy, drew laughter from the audience. But today, at NBCUniversal's headquarters at 30 Rockefeller Center, Scarborough's relationship with the Republican presidential frontrunner has become a subject of frustration among staff, and an increasingly problematic issue for the network's top brass.

Four of those sources also said that the growing media scrutiny over the two men's relationship has caused the network's leadership to more closely monitor Scarborough's comments. "The higher-ups are definitely aware about what's going on," said another person within MSNBC. "It's an issue."

Both Scarborough and co-host Mika Brzezinski are close friends with Trump and members of his family. Scarborough, a former four-term congressman from Florida's 1st district, has often stayed at Trump's Mar-A-Lago Club, in Palm Beach, Florida, with his family and was there during the week between Christmas and New Year's, two sources at the hotel during that time said.