Sen. Chuck Grassley (R-IA), the chairman of the U.S. Senate’s Judiciary Committee, has launched a probe into why the Department of Justice shut down efforts by federal law enforcement agents to investigate the Clinton Foundation.

The Clinton Foundation’s connections to actions that Hillary Rodham Clinton—the 2016 Democratic Presidential nominee—took as Secretary of State and the interests of its international high dollar donors has become a front-and-center discussion in the 2016 election. The “Clinton Cash” narrative first broke onto the scene in 2015 with the publication of the book by that name from Government Accountability Institute president and Breitbart News editor at large Peter Schweizer.

News reports have surfaced recently that FBI agents sought approval to formally investigate the Clinton Foundation, but that the Department of Justice’s attorneys—under the direction of Attorney General Loretta Lynch—shut them down. Subsequent reports, from The Daily Caller, have stated that the U.S. Attorney for the Southern District of New York Preet Bharara has launched his own investigation with federal agents into the Clinton Foundation.

But now, the U.S. Senate’s Judiciary Committee is getting involved, bringing a major player into the room that could rock the entire governmental structure currently shielding the Clintons. Grassley, notorious for his aggressive bulldog-like oversight style, wrote to Lynch seeking answers in a detailed 10-page Monday letter.

“While all of these circumstances are not proof of wrongdoing, they do raise reasonable suspicions and undermine the public’s confidence in the integrity of the State Department’s operations during Secretary (Hillary) Clinton’s tenure,” Grassley wrote to Lynch. “The American people are entitled to reassurance that these matters have received thorough and objective investigation. Yet, it appears that the DOJ has turned a blind eye and refused to investigate.”

Grassley specifically asked for details about when the Department of Justice declined to inquire into the Clinton Foundation, how it made the decision, and which political appointees were involved in the decision if any. He also, according to a press release, asked “whether the Justice Department evaluated the FBI’s recovery of thousands of work-related emails from Clinton’s non-governmental server as part of considering a public corruption case, and other related questions.”

“At this point, the American people and Congress are owed answers,” Grassley wrote to Lynch.

Read the full 10-page letter here.

It’s unclear whether the DOJ will cooperate with Grassley’s investigation, and if the DOJ blows him off as it has done in the past, what if anything Grassley will do to fight back.