He then described the demand as very disturbing.
The Senate committee is looking into the circumstances around Comey's dismissal and how they relate to the FBI investigation of Russian interference in the USA election. Much will be made of how the two men may have interpreted the phrase "honest loyalty" differently.
Noting that "I have not included every detail from my conversations with the President", Comey told lawmakers some striking details about "nine one-on-one" interactions he says he had with Trump over the course of four months.
"I have been very loyal to you, very loyal; we had that thing you know", Trump told Comey, according to the written testimony.
Lieberman cautioned that even if Comey's allegations are true, he would not yet consider it obstruction of justice.
Sen. John McCain, R-Ariz., asked Comey about it in the closing minutes of the hearing.
"I know that there are going to be members who want to hear from Deputy Attorney General Rosenstein about his involvement in the (Comey) firing", Senator Mark Warner, the top Democrat on the Intelligence Committee, told Reuters.
The committee released an advance copy of Comey's seven-page opening statement a day before his scheduled appearance. Comey said that he declined to do so in large part because of the "duty to correct" that would be created if that situation changed. Comey also alleges that the President asked him to stop investigating ex-national security adviser Michael Flynn and to publicly declare that Trump was not under investigation.
Comey will also tell lawmakers that he told Trump he was not personally under investigation, validating the president's previous claims that he was not the target of the probe into his campaign's possible ties to Russian Federation.
Comey's recent hearings on the Hill - before he was sacked - had offered some very stunning revelations. "He agreed, but then re-emphasized the problems this was causing him", Comey wrote. "Three in person and six on the phone". He said Trump could say he was merely vouching for Flynn's character and voicing concerns about how the probe was interfering with his ability to function as president.
"A few moments later, the President said, 'I need loyalty, I expect loyalty, '" one Twitter user wrote.
Dale Carpenter, a law professor and constitutional law chairman at Southern Methodist University, countered that any probe of a Trump aide's Russian contacts is linked to the overall examination of Russian involvement in last year's presidential election, an investigation that potentially could reach the president.
According to media reports, Comey met alone with Trump on a number of occasions and kept detailed memos of what was discussed.
White House officials had considered trying to invoke the President's executive privilege authority to block the testimony, but they said on Monday that they would not do so.
Comey, who is used to not answering lawmakers' questions about ongoing investigations, is not likely to say anything Thursday that could interfere with, or undercut, the ongoing federal investigation into Russian Federation ties. Clinton has blamed Comey's October 28 announcement that he was re-opening the email investigation for her defeat.
In the wake of the firing, the Justice Department named an special prosecutor, former FBI director Robert Mueller, to lead the government's investigation.
On Thursday the former Federal Bureau of Investigation director has at least two scenes to unfold, according to his opening statement.
The statement may provide political ammunition to Trump opponents, but unless they are willing to stretch Comey's words and take Trump's out of context and unless they are prepared to abandon important constitutional principles and civil liberties that protect us all, they should not be searching for ways to expand already elastic criminal statutes and shrink enduring constitutional safeguard in a risky and futile effort to criminalize political disagreements.