(CNN) A new cache of text messages exchanged between two top FBI officials that have come under fire for criticizing then-presidential candidate Donald Trump were delivered to lawmakers on Capitol Hill Friday evening, according to a letter from Republican Sen. Ron Johnson.

The delivery of nearly 400 pages of new text messages sent by FBI officials who were briefly on special counsel Robert Mueller's team sets up a new chapter in the political swirl of accusations that some members of the FBI working on the Russia probe are biased against Trump.

In a letter to FBI Director Christopher Wray on Saturday, Johnson -- the chairman of the Senate Homeland Security Committee -- described several of the texts that appear to involve the FBI's handling of Hillary Clinton's use of a private email server while secretary of state, a subject of investigation for the committee.

In one February 2016 exchange, FBI lawyer Lisa Page calls it "unbelievable" that the 2016 presidential race would come down to Clinton versus Trump. Peter Strzok, who led the investigation of the Clinton email server as the No. 2 official in the FBI's counterintelligence division, responds, "Now the pressure really starts to finish MYE . . . ," an apparent reference to "Midyear Exam" -- the FBI's internal case name for the Clinton investigation.

The Homeland Security Committee, as well as at least two House panels and the Justice Department's Office of Inspector General, are all independently examining the FBI's conduct of the investigation and actions surrounding the Clinton investigation.

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