Attorney General William P. Barr has subsequently portrayed the entire investigation as illegitimate. Senators are expected to ask Mr. Rosenstein whether, knowing what he knows now, he would have appointed Mr. Mueller.
Rosenstein had a role in a plagued set of wiretap applications.
In December, the Justice Department’s independent inspector general, Michael E. Horowitz, released a damning report about errors and omissions by the F.B.I. in applications to obtain a national security wiretap order targeting Carter Page, a former Trump campaign adviser, in October 2016, as well as three renewal orders in 2017.
The Justice Department has subsequently told a court it did not think the available evidence met the legal standard to keep invading Mr. Page’s privacy for the last two renewals. Mr. Rosenstein signed off on the third and final renewal application for that surveillance, and senators are expected to question him about the matter.
The hearing is just a start for Republicans’ plan to showcase investigators’ missteps.
Mr. Trump, who is portraying the effort to understand the scope of Moscow’s covert manipulations and the nature of his campaign’s links to Russia as a partisan conspiracy to sabotage him, sees rewriting the narrative of the Russia investigation as a key to his re-election campaign. Republicans are keen to use their Senate majority to help.
On Thursday, Mr. Graham and Senator Ron Johnson, Republican of Wisconsin and the chairman of the Homeland Security and Governmental Affairs Committee, both plan to ask their respective panels to grant them substantial powers to issue subpoenas for reams of records related to the Russia investigation and for testimony from dozens of current and former law enforcement and national security officials, including prominent Obama administration officials.
Among them are Mr. Comey; former Attorney General Loretta E. Lynch; Susan E. Rice, President Barack Obama’s national security adviser; Denis R. McDonough, Mr. Obama’s chief of staff; and Andrew G. McCabe, Mr. Comey’s deputy who helped steer the investigation after he was fired.
The issues in question have already been exhaustively studied by Mr. Horowitz and are still being scrutinized by a federal prosecutor, John H. Durham, whom Mr. Barr handpicked to examine his concerns about the investigation. But where those inquiries largely take place out of view, Mr. Graham and Mr. Johnson are planning public hearings throughout the summer leading up to this fall’s elections that will emphasize the ways they believe Mr. Trump was mistreated.