The top Democrat on the House Oversight Committee is pushing back on a Republican investigation into the 2010 sale of a uranium company with holdings in the U.S. to the Russian nuclear giant Rosatom.

Minority members learned of the investigation when Rep. Ron DeSantis (R-Fla.) announced the probe on television last month, ranking member Rep. Elijah Cummings (D-Md.) wrote in a Tuesday letter to chairman Trey Gowdy (R-S.C.).

Since then, he says, the committee has taken no investigative steps "at least as far as I am aware."

"These actions raise serious questions about whether Republicans are reopening this investigation of Hillary Clinton for the same illegitimate reasons that President Trump demanded it - to try to distract public attention from the ongoing criminal probe into President Trump's campaign and its ties to Russia," Cummings wrote.

The investigation - formally announced late last month by DeSantis and Intelligence Committee Chairman Devin Nunes (R-Calif.) - retreads familiar ground for Republicans, who have used the issue of the sale to try to discredit former Democratic presidential candidate Hillary Clinton since it was revealed in conservative author Peter Schweitzer's 2015 book "Clinton Cash."

The approval for the takeover was inked by a nine-agency review board that included the State Department when Clinton was secretary of State.

The company, Uranium One, at the time controlled land equal to about 20 percent of the U.S.'s uranium capacity - although experts note that the U.S. doesn't actually produce a significant amount of the world's uranium stock. Rosatom began buying shares in the Toronto-based company in 2009 and in 2010 sought to obtain majority ownership, a deal which required the review board's approval.

Republicans have long accused the former secretary of tying the State Department's approval of the takeover to $145 million in donations to the Clinton Foundation.

The State Department did not take unilateral action but instead was one of the nine agencies on the review board, known as the Committee on Foreign Investment in the United States (CFIUS). The Clinton campaign has maintained that the then-secretary of State was not directly involved in the process.

Republicans say their concerns were stonewalled by the Obama administration at the time and now they want to know whether the deal should have been approved in the first place.

In a statement Tuesday, Gowdy insisted that the investigation "is not about one individual."

"It is about whether or not all pertinent information was known and shared with CFIUS at the time they made their decision and whether the actions of Russia in 2015 and 2016 should cause the U.S. to reevaluate Russia's motives in 2010," he said.

According to DeSantis, a confidential informant has come forward who he believes "would be able to link" half a million dollars paid to former President Bill Clinton for a speech from sources connected with Uranium One.

"Millions of dollars to the Foundation from sources connected with Uranium One. And then you have the approval of the deal on the CFIUS board, which Hillary Clinton was a member of, in 2010," DeSantis told Fox News in October.

"So you do have the quid, you have the quo. This informant, I believe, would be able to link those two together."

The informant came forward to both the House Oversight and Government Reform and House Intelligence committees.

In October, DeSantis and Nunes said the two panels were in discussions with the Justice Department to release that individual from a nondisclosure agreement.

According to Cummings, Justice cleared the individual to speak to the committee on October 25 "but Chairman Gowdy has failed to bring him in."

Cummings on Tuesday demanded that Democrats have access to that confidential informant.

According to Cummings, the Oversight Committee already investigated the matter years ago and "identified no evidence that Secretary Clinton improperly influenced the process to cause the nine CFIUS member agencies to approve the deal."

In June of 2015, according to Cummings, DeSantis and then-Oversight chair Jason Chaffetz (R-Utah) sent 14 document requests to all nine CFIUS member agencies, as well as the five CFIUS observer offices, which included the National Security Council, the National Economic Council and others.

The committee received a classified briefing related to the transaction in November of that year, according to Cummings, and staff made a trip to the Treasury Department to review classified documents in a secure setting. The agency provided several other rounds of classified documents to the committee that Cummings said "satisfied" the panel.

Several other congressional committees including the House Financial Services Committee and two powerful Senate committees also investigated the matter.

"The committees that conducted these reviews identified no evidence to substantiate allegations that Secretary Clinton orchestrated, manipulated, or otherwise coerced CFIUS member agencies to approve the deal," Cummings wrote.

"In contrast, they all dropped their investigations without further action, stopped sending letters, and never issued a report of their findings."

Republicans say they first want to know whether there was an FBI investigation into Russian efforts to infiltrate the U.S. energy market, which at the time included assuming shares of the uranium company, Uranium One.

The announcement of the investigation came shortly after The Hill reported that the FBI had gathered evidence that Moscow had compromised an American uranium trucking firm with bribes and kickbacks as part of an effort to grow Russian President Vladimir Putin's atomic energy business inside the United States - an investigation that predated the approval of the Uranium One sale.