Then-Iowa Republican senatorial candidate and former U.S. Attorney Matt Whitaker watches before a live televised debate in Johnston, Iowa, April 24, 2014. Credit: Charlie Neibergall | AP

WASHINGTON — The Senate’s top Democrat has asked the Justice Department’s inspector general to investigate acting Attorney General Matthew Whitaker’s communications with the White House, over concerns that he might have shared secret information from special counsel Robert Mueller’s investigation with President Donald Trump.

In a letter to Justice Department inspector general Michael Horowitz, Senate Minority Leader Charles Schumer, D-New York, asked him to open a formal probe into whether there have been any “unlawful or improper communications” between Whitaker and the White House during his service as former attorney general Jeff Sessions’s chief of staff, when he was in regular touch with Trump and White House Chief of Staff John Kelly.

In particular, Schumer said he was concerned that as acting attorney general, Whitaker could share “confidential grand jury or investigative information from the Special Counsel investigation or any criminal investigation.”

Schumer also wants Horowitz to investigate whether Whitaker “provided any assurance to the President, White House officials, or others regarding steps he or others may take with regard to the Special Counsel investigation, including any intention to interfere, obstruct, or refuse authorization of subpoenas or other investigative steps.”

In the course of Mueller’s probe, federal law enforcement officials have been looking into members of the Trump campaign’s alleged contacts with Russian officials or their intermediaries.

The probe has already resulted in indictments or plea deals for former Trump lawyer Michael Cohen, former Trump campaign chairman Paul Manafort, former campaign aide Rick Gates, former campaign adviser George Papadopoulos and former national security adviser Michael Flynn, along with a host of Russian officials and operatives.

Congressional Democrats have been concerned that Whitaker, who has supported the president’s unbridled criticism of Mueller’s probe, may have been named as Sessions’s successor to oversee its undoing. Many have called for Whitaker to recuse himself, while some sued this week to challenge his appointment as unlawful.

Following a meeting with Whitaker last week, Sen. Lindsey Graham, R-South Carolina — a recent Trump ally and the likely heir apparent to lead the Senate Judiciary Committee next year — said he was sure Whitaker would not do anything “draconian” to Mueller’s probe.