A key Republican chairman is trying to dramatically widen Senate Republicans' probe into how the FBI handled the investigation into Hillary Clinton's use of a private email server, and the top Democrat on his committee is branding the effort an “orchestrated, partisan smear.”

Senate Homeland Security Committee Chairman Ron Johnson, R-Wis. is participating in a badly political attack on “the FBI and our federal law enforcement officials,” said a spokesman for Sen. Claire McCaskill, the most senior Democrat on the committee.

“Senator McCaskill hoped that last week’s unsubstantiated rants about secret societies and informants would have caused the Chairman to take pause, but instead he’s forging ahead,” said her spokesman Drew Pusateri.

“The Homeland Security and Governmental Affairs Committee has a long history of aggressive, bipartisan, important oversight—but it’s also served as a warning of what happens when Congress wields its authority as an ideological weapon—and the actions we’ve seen in the last week are deeply troubling.”

Johnson Thursday asked the Department of Justice to turn over texts, emails, memos and voicemails from 16 FBI and DOJ officials, including former Director James Comey, former Deputy Director Andrew McCabe and outgoing Chief of Staff Jim Rybicki.

In a letter to Deputy Attorney General Rod Rosenstein posted on the committee’s website, Johnson demanded the communications from employees between Jan. 1, 2015, to the present.

The request stems from text messages between FBI official Peter Strzok and FBI lawyer Lisa Page which were already turned over to the committee.

Johnson noted in his letter that in those texts, Page and Strzok — who were reportedly having an affair — made reference to communicating with other FBI employees via text message, phone calls and email.

Additional text messages also suggest that FBI officials used non-official email accounts and messaging programs to communicate about official business, Johnson said.

His letter also requests emails between 2016 Democratic presidential nominee Hillary Clinton and former President Barack Obama that Johnson says were exchanged while Clinton was in the “territory of a sophisticated adversary.”

McCaskill is running for re-election this year in Missouri, a state Trump won by nearly 20 percentage points. But it’s not the first time that McCaskill has been critical of her Republican counterpart. The former Missouri prosecutor also criticized Johnson recently for raising the specter of a “secret society” at the FBI plotting against President Donald Trump. Johnson later conceded the “secret society” reference may have been a joke between the two FBI agents.

“If the committee has any evidence that the FBI is, as you have stated, biased and corrupt at the highest levels, I assume that evidence is strong in both quality and quantity, and extends far beyond a casual mention in a text message between two agents who were involved in personal crosstalk,” McCaskill wrote to Johnson.

Johnson previously wrote to F.B.I. Director Christopher Wray on January 20 requesting information on missing text messages between F.B.I. Strzok and Page, and how the F.B.I. oversees private accounts for official business.

Strzok, a counterintelligence agent who worked the Clinton email case, last summer was taken off the FBI team investigating whether there are ties between Russia and Trump's presidential campaign after text messages surfaced between Strzok and Page that were derogatory of Trump.

Page had left Special Counsel Robert Mueller's team before the text messages were found.

The request for new documents come as Johnson and the House Judiciary and Oversight and Government Reform committees have launched inquiries into the FBI’s handling of the investigation into Clinton's use of a private email server as Secretary of State, including why former FBI Director James Comey did not recommend criminal charges against Clinton.

Democrats have accused Republicans of mounting the investigations with the aim of raising doubt about the FBI's impartiality and deflecting attention from the special counsel’s probe into whether President Donald Trump’s campaign conspired with Russia.

The FBI’s performance is also the subject of an independent investigation by the Justice Department’s internal watchdog agency, which began looking into it in January 2017.