"I need loyalty, I expect loyalty," Mr Comey quotes the US President telling him.
Asking for loyalty isn't illegal, unethical or immoral, and most certainly not the grounds for impeachment.
But translators of Trump-speak see it more as a threat than an appeal when given to the supposedly independent head of the FBI. It goes beyond the merely inappropriate behaviour of the President.
However, Mr Trump will be a spectator to the information-gathering committee proceedings, where his name will appear frequently. And it will all be a test of his discipline.
President Trump is not expected to take things calmly and the prospect is for a continued commentary being tweeted from the White House as the questions are asked. At worst, the President might actively attack witnesses and the committee panel.
Roger Stone, the veteran political adviser who taught Mr Trump his "admit nothing, deny everything" strategy, expects a counterpunch.
"He's not going to take an attack by James Comey laying down," Mr Stone told The Washington Post.
"Trump is a fighter, he's a brawler and he's the best counterpuncher in American politics."
While appealing to Mr Comey to show loyalty is not illegal, there are other matters which could be critical. Urging an FBI investigator to go easy on a White House colleague could be illegal if it is found to amount to obstruction of justice.
"I want to talk about (former national security adviser) Mike Flynn," Mr Comey quotes Mr Trump saying in private talks on February 14.
Mr Flynn had left the previous day after it was revealed he had lied about meeting Russian ambassador to the United States, Sergey Kislyak.
"I hope you can see your way clear to letting this go, to letting Flynn go. He is a good guy. I hope you can let this go," the President said, according to Mr Comey.
The damage to his administration already is considerable.
The size of the Washington crowd cheering on the President shrinks further every day, as the hostility towards him increases. And it's not just Democrats who are his enemies.
Mike Murphy, a political consultant who worked for failed Republican presidential hopeful Jeb Bush, is a bitter voice from within the party establishment.
On June 4 he tweeted: "The next ten years of US Foreign policy will be spent repairing the damage this fool is doing and the easy wins he's giving our opponents."
And this on June 6: "Such a tiny man we have in the WH. @realDonaldTrump is wholly consumed by his petty insecurities."