Former Deputy Attorney General Rod Rosenstein told lawmakers Wednesday that he would not have approved an FBI surveillance application for a former Trump campaign aide during the Russia investigation had he known at the time about the problems that have since been revealed. Rosenstein's comments amounted to a striking concession that law enforcement officials made mistakes as they scrutinized ties between Russia and Donald Trump's 2016 presidential campaign. But even as he acknowledged the legitimacy of anger from Trump and his allies, he defended his appointment of special counsel Robert Mueller to lead the probe and affirmed his support for the conclusion that Russia interfered in the election but did not criminally conspire with associates of the Trump campaign. “I do not consider the investigation to be corrupt, Senator, but I certainly understand the president’s frustration given the outcome, which was in fact that there was no evidence of conspiracy between Trump campaign advisers and Russians,' Rosenstein said at a hearing of the Senate Judiciary Committee. His appearance before the committee was the first in a series of hearings scrutinizing the FBI’s Russia investigation and the law enforcement officials involved. With subpoena authority expected to be approved this week, the hearing marked the opening salvo of the GOP's election-year congressional investigation into what they say are damaging findings about the Russia probe from a Justice Department inspector general review. The president's allies have taken fresh aim at the Russia investigation over the last year, pointing to newly declassified information to allege that Trump and his associates were unfairly pursued. They have claimed vindication from the Justice Department's decision to dismiss the case against ex-national security adviser Michael Flynn while at times advancing unsupported theories against Obama administration officials. “We’re going to look backward so we can move forward,' committee chairman Sen. Lindsey Graham, R-S.C., said in explaining the hearings' purpose. “If you don’t like Trump, fine, but this is not about liking Trump or not liking Trump. This is about us as a nation.' Graham also questioned whether Mueller should have been appointed at all. Rosenstein, who appointed Mueller in May 2017, said he believed there had been a sufficient basis for the investigation and for the naming of a special counsel. But when Graham asked if he would agree with the general statement that by August 2017, there was “no there there' when it came to a criminal conspiracy between Russia and Trump, Rosenstein said yes. Democrats lamented the hearing's politically charged and retrospective nature, saying Republicans were attempting to refocus attention away from more urgent problems, including unrest in cities set off by the death of George Floyd and the coronavirus pandemic. “This hearing wastes this committee’s time in a blatant effort to support the president’s conspiracy theories and to help the president’s reelection,” said Democratic Sen. Mazie Hirono of Hawaii. The hearing delved into detail in two areas that Trump allies have recently seized on to challenge the conduct of law enforcement. Rosenstein was pressed repeatedly about his decision to sign off on the fourth and final application for a warrant to eavesdrop on Trump campaign adviser Carter Page on suspicion that he was a Russian agent. Page has denied wrongdoing and was never charged with a crime, and a Justice Department inspector general report identified significant errors and omissions in each of the applications submitted to the Foreign Intelligence Surveillance Court. The watchdog said the FBI relied in part for its applications on a dossier of information compiled by a former British spy whose research was funded by Democrats and the Hillary Clinton campaign. The FBI used the dossier even though agents were aware of the possibility that it could have been colored by Russian disinformation, and an FBI lawyer is suspected of altering an email related to the application process, according to the inspector general. Asked by Graham if he would have signed the warrant application if he knew then what he knows now, Rosenstein replied, “No, I would not.' Rosenstein said he was unaware of the problems when he approved the final application in June 2017, echoing an inspector general finding that senior FBI officials were given incomplete information. He said he actually considered the application he approved fairly persuasive but conceded he had not read every page, noting that the warrant had already been approved multiple times before it reached him. Although Rosenstein was a Trump appointee, he has often been regarded with suspicion by many supporters of the president, and Trump himself, for his role in the investigation. Rosenstein's fate was most dramatically in limbo in September 2018 after it was reported that he had floated the idea of wearing a wire inside the White House to record conversations with Trump. Rosenstein denied Wednesday having ever suggested secretly recording Trump. Rosenstein was also pressed about his oversight of Flynn's guilty plea with the Mueller team. Flynn admitted lying to the FBI about his conversations with the Russian ambassador during the presidential transition period regarding U.S. sanctions. The Justice Department moved to dismiss the case last month, saying that Flynn's contacts with the diplomat were appropriate and that the FBI had insufficient basis to interview him, especially since agents had been prepared weeks earlier to close their investigation into Flynn after finding no evidence he had broken the law. Rosenstein said he had no recollection being told the FBI had planned to close the Flynn inquiry before the interview, but said that fact would have mattered to him. The Judiciary Committee plans to vote Thursday on whether to authorize subpoenas for dozens of current and former officials involved in investigating Russian election interference, including former FBI Director James Comey and ex-CIA Director John Brennan. ___ Associated Press writer Mary Clare Jalonick in Washington contributed to this report.