Deputy Attorney General Rod Rosenstein wrote the memo the president initially cited as justification for firing FBI Director James Comey.
The deputy attorney general stood by the contents of his memo in his comments to Congress on Thursday, maintaining his disagreement with Comey's actions in relation to the investigation of Hillary Clinton's emails as secretary of state, according to Rosenstein's prepared opening statement to both the House and Senate.
Committee leaders said on Friday he would appear sometime after the U.S. Memorial Day holiday on May 29.
Mr Trump has fervently denied that his campaign collaborated with Russian Federation or that he tried to shut down an FBI probe of the issue - and claimed to be the most hounded president in history, calling the investigation a "witch hunt".
Speaking to NBC News' Lester Holt on May 11, Trump mentioned the Russian Federation investigation when explaining why he fired Comey, whom he called a "showboat" and a "grandstander".
To the editor: In the Oval Office on February 14, Trump asked then-FBI Director James Comey to be his special valentine and shut down the investigation of his BFF, the recently fired national security advisor Michael Flynn.
That does absolutely nothing to help Trump with the pervasive speculation that he fired Comey because of the investigation into his Russian ties.
Trump, who has embraced what he describes as an "America First" approach to USA foreign policy and worldwide trade, is expected to be welcomed warmly by leaders in Saudi Arabia and Israel.
Earlier this week, Deputy Attorney General Rod Rosenstein appointed ex FBI Director Robert Mueller to serve as special counsel and lead the investigation into Russian meddling. and whatever else they find.
But Rosenstein confirmed to lawmakers that he learned of Trump's decision to fire Comey one day before writing the memo outlining his perceived misconduct.
Massachusetts Democratic congressman Seth Moulton says Rosenstein didn't "do a lot to bolster our confidence in him".
Rosenstein in his remarks to Congress today echoed the contents of the memo he sent to Trump in his criticism of the former FBI chief's handling of the Clinton email probe, including Comey's press conference last July about the investigation.
"I wrote it. I believe it".
Mueller joined me and two of my staff for an informal lunch in a cafe where we discussed some of these issues.
Asked point-blank Thursday if he'd done anything that might merit prosecution or even impeachment, Trump said no - and then added of the lingering allegations and questions: "I think it's totally ridiculous". Sessions has recused himself from the Trump-Russia probe, citing his close involvement in the Trump campaign previous year.
The appointment of the special counsel indicates other believe that's still open to question.
A number of lawmakers said Rosenstein also told them that Comey hadn't asked for more resources for the Russian Federation investigation before he was sacked as some reports had indicated. Rosenstein denounced that as "profoundly wrong and unfair".