The Justice Department inspector general says he has recovered missing text messages from two senior FBI officials who investigated Hillary Clinton and Donald Trump and exchanged notes critical of the president.

In a letter to congressional leaders, Inspector General Michael Horowitz said his office "succeeded in using forensic tools" to recover messages between senior FBI agent Peter Strzok and FBI lawyer Lisa Page during a key five-month period ending the day special counsel Robert S. Mueller III was appointed to investigate possible coordination between the Kremlin and Trump's campaign. The missing messages have sparked a political firestorm in recent days, with GOP leaders and the president questioning how the FBI failed to retain them.

Horowitz's letter did not indicate how many messages were recovered, and it said his effort to locate more was "ongoing." He said he would provide copies to the Justice Department and would not object if leaders there determined it was appropriate to turn them over to Congress. A Justice Department official has said that the FBI failed to save text messages sent from thousands of cellphones, including Page's and Strzok's.

Top FBI official assigned to Mueller’s Russia probe said to have been removed after sending anti-Trump texts (The Washington Post)

The letter was sent to Sen. Charles E. Grassley (R-Iowa), chairman of the Senate Judiciary Committee, and Sen. Ron Johnson (R-Wis.), chairman of the Homeland Security and Governmental Affairs Committee.

Horowitz has been investigating Strzok's and Page's conduct as part of a broader examination of the probe into Clinton's use of a private email server while she was secretary of state. Both worked on the Clinton case and the probe, led by Mueller, into whether Russian agents may have coordinated with Trump associates during the 2016 presidential election.

On Thursday, Grassley released some previously recovered texts from the pair discussing the Clinton case — and calling into question whether she had been treated too gently. During one February 2016 exchange in which the two discussed the number of agents and prosecutors involved, Page remarked of the former secretary of state: "One more thing: she might be our next president. The last thing you need us going in there loaded for bear. You think she's going to remember or care that it was more doj than fbi?"

In March 2016, Strzok and Page seemed to discuss the possibility of Patrick Fitzgerald, a former federal prosecutor now in private practice, being appointed as a special counsel to oversee the matter.

In a set of messages exchanged Oct. 28, 2016, Page and Strzok discussed Page's boss, FBI Deputy Director Andrew McCabe, and an upcoming story in the Wall Street Journal documenting concerns inside the FBI about his oversight of investigations into Clinton and the Clinton Foundation.

Page texted that James Rybicki, the chief of staff to then-FBI Director James B. Comey, "clearly 100% believes that Andy should be recused because of the 'perception.' '' Strzok replied "God," and the two expressed bafflement that the FBI would reverse its position on the matter. At the time, the FBI had publicly defended McCabe — whose wife had run for political office in 2015 and accepted donations from a Clinton ally — and said there was no reason to recuse.

Grassley wrote in a letter that the messages "raise serious concerns about the impartiality of senior leadership running both the Clinton and Trump investigations."

The Washington Post reported in December that Strzok was removed from the Trump probe in July 2017 after internal investigators discovered he and Page, who were romantically involved, exchanged anti-Trump, pro-Clinton texts during investigations of both political figures. Page had left the Mueller team two weeks before Strzok for what officials said were unrelated reasons.

In recent weeks, the Justice Department has provided Congress with hundreds of pages of their messages, and Republicans said the texts revealed political bias at the bureau's highest levels. Democrats have accused Republicans of seizing on the issue in an effort to derail or delegitimize the Russia investigation — accusing conservatives of trying to discredit the FBI as they seek to protect the president.

Congress was notified last week that the FBI could not find five months' worth of texts between the two officials — which President Trump and others met with skepticism.

"That's a lot of missing texts, and as I said yesterday, that's prime time," Trump said Wednesday. "So, you do sort of look at that and say, 'What's going on?' "

The last day of missing texts, May 17, coincided with Deputy Attorney General Rod J. Rosenstein's decision to appoint Mueller as special counsel overseeing the Russia investigation.

Much occurred during the months leading up to that day. Comey met repeatedly with Trump, the Russia probe intensified and began to focus on former national security adviser Michael Flynn, and, in early May, Trump fired Comey.

The FBI had told the Justice Department that "many FBI-provided Samsung 5 mobile devices did not capture or store text messages due to misconfiguration issues related to rollouts, provisioning and software upgrades that conflicted with the FBI's collection capabilities," a Justice Department official told lawmakers in a letter earlier this month.

As a result, the letter said, "data that should have been automatically collected and retained for long-term storage and retrieval was not collected.''