Members of Congress write a lot of letters. Often, they make a big show of it. Usually, nothing more is ever heard.

But according to ABC News, a letter coauthored by Sen. Patrick Leahy (D-Vt.) and then-senator Al Franken (D-Minn.) may have touched off a Federal Bureau of Investigation inquiry into whether Attorney General Jeff Sessions lied during his January 2017 confirmation hearing.

Leahy and Franken sent the letter in March 2017 to then-FBI director James Comey, asserting that Sessions had provided testimony that "appears to be discernibly false" regarding his contacts with the Russian government or its officials, which may have constituted perjury.

The senators asked Comey to "investigate all contacts the Russian ambassador, or other Russian officials, may have had with Attorney General Sessions or with his staff, and whether any laws were broken in the course of those contacts or in any subsequent discussion of whether they occurred."

Leahy and Franken sent a follow-up letter to Comey on April 28, shortly before he was fired by President Donald Trump. They sent a third letter two weeks later to then-acting FBI director Andrew McCabe, seeking an update.

ABC News reported Wednesday that McCabe authorized an investigation into whether Sessions had misled members of Congress during his confirmation hearing. Sessions fired McCabe, then the FBI deputy director, last Friday.

One source told ABC News "that Sessions was not aware of the investigation when he decided to fire McCabe." The ABC report cited "sources familiar with the matter."

ABC also reported that sometime last year, "several top Republican and Democratic lawmakers were informed of the probe during a closed-door briefing with Deputy Attorney General Rod Rosenstein and McCabe."

In mid-May, Rosenstein appointed former FBI director Robert Mueller as special counsel to investigate Russian efforts to influence the 2016 presidential election and any coordination between Russian officials and the Trump campaign. Mueller's charge included any involvement by Sessions.

David Carle, a Leahy spokesman, said Wednesday that the senator was not notified of the reported inquiry into Sessions.

"On May 31, 2017, the FBI responded that it could neither confirm nor deny the existence of an investigation," Carle said in a statement. "Senator Leahy was not otherwise made aware of an investigation."