Trump demanded loyalty to Comey three days after the FBI interviewed Michael Flynn over Russia

Three days after the FBI interviewed Michael Flynn about his ties with Russia, and nne day after former acting Attorney General Sally Yates warned Donald Trump about the fact that Michael Flynn could be blackmailed by Russia, Donald Trump called James Comey to a dinner at the White House and demanded that Comey pledged loyalty to Trump.

The FBI interview took place on January 24, 2017. Yates warned Trump on January 26. On the 27th, Trump called Comey and demanded that he pledged his loyalty to him.

By the way: Sean Spicer denied Trump asked Comey for loyalty, but an associate of Comey confirmed the request for loyalty did take place. According to AP:

Press secretary Sean Spicer is refuting that account during his daily briefing. He says the president wants “loyalty to this country and to the rule of law.”

An associate of the fired FBI director confirmed Friday that Trump asked for Comey’s loyalty during the private dinner. The associate with knowledge of the conversation confirmed an account of the conversation in The New York Times is accurate.

During the dinner, Comey refused to pledge his loyalty and instead offered the president his honesty.

Which suggests the following: That Trump got nervous because he knew the Russia investigation was getting close, and that's why he demanded loyalty from Comey. He didn't get the loyalty he wanted, and that's why he fired Comey.