Sen. Chris Murphy is requesting an investigation into whether certain federal agencies are demonstrating political bias by complying with Republican-led requests related to Hunter Biden and the Ukrainian gas company Burisma.

In a letter set to be sent Wednesday to inspectors general for the State Department, the Treasury Department, the Department of Homeland Security and the National Archives, the Connecticut Democrat expressed concern that the agencies were cooperating with Republican-led investigations connected to former Vice President Joe Biden’s son. But he said those same agencies didn’t comply with congressional investigations into President Donald Trump.

“It just looks to me like there's a really concerning double standard -- these agencies said ‘no’ to every document request related to the investigation of President Trump but they may be willing to cough up anything that Senate Republicans are asking them to produce on the Biden family,” said Murphy in an interview.

Johnson and Senate Finance Committee Chair Chuck Grassley (R-Iowa) have also requested the State Department release any documents related to Hunter Biden. In addition, they've asked the National Archives and Records Administration for records of any White House meetings in 2016 between Obama administration officials, representatives of the Ukrainian government and the Democratic National Committee officials, as part of an effort to investigate Ukraine's role in the 2016 election. There's no evidence of a top-down effort from the Ukrainian government to interfere U.S. politics.

Murphy, in the interview, said it’s not coincidental that Senate Republicans are ramping up their probe following Biden’s surge in the Democratic primary.

“Our responsibility is to make sure that the official letters of the government aren't used to destroy people's political opponents — that seems to be a theme in this administration,” Murphy said. “I expect Democrats are going to have to spend time explaining why it's illegitimate for Senate Republicans to use their position to try to destroy the Bidens.”

In his letter, Murphy requests that the inspectors general explain whether their agency has cooperated with any congressional requests related to Hunter Biden or Burisma; the extent of their compliance; if the agency cooperated with other congressional requests, including probes Trump’s tax returns; and if there have been different standards applied for probes into Trump’s political opponents compared to probes into the president.

He requested a response by March 23.