Sen. Chris Murphy (D-CT) expressed deep concerns on Wednesday that federal agencies are cooperating with the GOP investigations into the Burisma Holdings-linked Ukraine dealings of Democrat 2020 presidential front runner Joe Biden and his son Hunter.

The Democrat senator suggested that political bias is driving the probes.

In a letter sent on Wednesday to the inspectors general for U.S. National Archives as well as the Departments of Treasury, State, and Homeland Security, Murphy called for a probe of the agencies that are doing their jobs and complying with the GOP investigations, demanding a response by March 23.

Meanwhile, Senate Homeland Security Committee Chairman Ron Johnson (R-WI), who is leading one of the Burisma-Biden probes, is pressing the National Archives to release more documents, the Washington Examiner reported Wednesday.

Murphy wrote in his letter:

I am deeply concerned that the National Archives and the Departments of State, Treasury and Homeland Security may not be applying a consistent test regarding inquiries made by Congress, choosing to comply with the requests that are designed to damage the president’s political opponents, but refusing to comply with requests into the activities of the president. This double standard threatens to make these agencies agents of the president’s political campaign, in contravention of federal law.

The Connecticut Democrat suggested that President Donald Trump has weaponized government agencies to combat his political rivals.

He wrote:

I am troubled that President Trump may be weaponizing the executive branch in advance of the 2020 elections by directing agencies to comply with congressional investigations designed to hurt his political opponents while stonewalling legitimate oversight investigations into the actions of his own administration. … It is critical that executive branch agencies remain apolitical and not be made agents of a president’s political operation or reelection campaign.

Echoing the letter during an interview with Politico, Murphy complained of a “double standard” when it comes to agencies complying with congressional probes, saying:

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.

As part of their investigations into the Bidens, Johnson and Senate Finance Committee Chairman Chuck Grassley (R-IA) have sought documents from the Departments of State, Treasury, and Justice, as well as the Secret Service, the National Archives, and Blue Star Strategies, a lobbying firm employed by Burisma.

Hunter took a job serving on the board of directors of the allegedly corrupt energy company Burisma while his father was leading U.S. policy towards Ukraine, including anti-corruption efforts.

The White House hopeful’s son worked for Burisma between 2014 and 2019 despite individuals from inside and outside the Obama administration raising conflict of interest and corruption concerns.

In October 2019, Hunter admitted that his father’s position as Vice President of the United States helped him secure the lucrative job at Burisma, which paid him $83,000 per month.

The Bidens have denied any wrongdoing. Johnson has cited the lack of investigations into the Bidens’ dealings in Ukraine as the reason the allegations of corruption remain unfounded.

Grassley and Johnson have urged Senate Foreign Relations Committee Chairman Jim Risch (R-ID) to launch his own Biden-Ukraine probe.