Speaker of the House Paul Ryan said he "obviously" does not think it was appropriate for Donald Trump to ask former FBI Director James Comey for "loyalty".
"FBI Directors are supposed to be independent, that's something that's very, very critical," said Mr Ryan.
Mr Comey is set to testify in front of the Senate Intelligence Committee on memos he wrote detailing conversations with the President and the bureau's investigation into alleged ties between the Trump campaign team and Russia.
Mr Ryan, a Republican, was responding on MSNBC to questions about Mr Comey's prepared opening statement in which he states that Mr Trump said: "I need loyalty, I expect loyalty" during one the pair's meetings.
Mr Comey said the President would "always get honesty".
The Speaker said that Mr Comey's "substance seems to me...similar to what we've already been hearing."
Mr Ryan said Christopher Wray, the possible replacement for Mr Comey, fits the bill for someone who will be an independent "prosecutor, career professional type...but we also expect the position is treated independently and [what Mr Trump did] obviously crosses that".
The President is reportedly going to be watching the testimony from the White House dining room, surrounded by his legal team and some advisers. There was also a report that Mr Trump will be live-tweeting the event as well, according to the Washington Post.
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