Sen. Chuck Grassley Charles (Chuck) Ernest GrassleySenate Republicans face tough decision on replacing Ginsburg What Senate Republicans have said about election-year Supreme Court vacancies Biden says Ginsburg successor should be picked by candidate who wins on Nov. 3 MORE (R-Iowa) fired back Thursday at Minority Leader Harry Reid Harry Mason ReidSenate Republicans signal openness to working with Biden Mellman: The likely voter sham Bottom line MORE for criticizing his probe into former Secretary of State Hillary Clinton Hillary Diane Rodham ClintonWhat Senate Republicans have said about election-year Supreme Court vacancies Bipartisan praise pours in after Ginsburg's death Trump carries on with rally, unaware of Ginsburg's death MORE.

"I want to ... respond to Sen. Reid's juvenile attacks on my Judiciary Committee's investigations and to Sen. Reid's frequent crying about my previous State Department holds," said Grassley, who chairs the Senate Judiciary Committee.

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The Iowa Republican's comments come after Reid said this week that Grassley's committee "continues to waste millions of dollars" on opposition research against Clinton in her White House run.

Grassley, however, said Reid's comments "ring hollow" and are "nonsense."

"Let me empahsize, the Judiciary Committee cannot ignore these important issues simply because the former secretary decided to run for president," he said. "To be perfectly clear, I started this investigation before Secretary Clinton announced her candidacy."

Grassley has been at the center of the Senate's investigation into Clinton's private email server while at State. He has sent multiple letters to top administration officials, as well as attorneys for a former employee responsible for overseeing the server. He also previously had holds on approximately two dozen State Department nominees, over what Grassley said was a slow response to his request for documents, including on Clinton and a top aide. The rhetorical battle over Clinton comes as the two senators have been locked in a separate fight over the Supreme Court.

Reid has taken to the Senate floor on a near daily basis to lambast Grassley and the GOP strategy to fill the late Justice Antonin Scalia's vacant seat after the 2016 elections have taken place. Democrats remain adamant that Republican leadership will eventually cave and give Supreme Court nominee Merrick Garland a hearing and a vote.

Grassley, on Thursday, asked, "How much taxpayer money does Sen. Reid spend having his staff write daily speeches trying to undermine the work of the Judiciary Committee?"