Deputy Attorney General Rod Rosenstein vowed on Tuesday that the Justice Department "is not going to be extorted" by certain critics, and he depicted as cowards a group of Republicans who have drafted articles of impeachment against him."I just don't have anything to say about documents like that that nobody has the courage to put their name on and leak it in that way," Rosenstein said Tuesday in response to a reporter's question, a day after news outlets first reported on the draft authored by the pro-Trump House Freedom Caucus At the center of the Republican group's concern over Rosenstein is his role last year in approving continued covert surveillance of Trump associate Carter Page , who had previously been under FBI investigation after Russian spies tried to recruit him.Rosenstein is overseeing special counsel Robert Mueller 's probe into possible collusion between the Russian government and associates of President Donald Trump, and Republicans have been demanding the Justice Department turn over a cache of documents related to the surveillance of Carter and other matters tied to the 2016 presidential election In an interview with The Washington Post, the head of the House Freedom Caucus, Rep. Mark Meadows, R-N.C., called impeachment proceeding against Rosenstein "a last resort option, if the Department of Justice fails to respond" to his requests for documents.Speaking Tuesday at a discussion series about "The Rule of Law" in Washington, Rosenstein said the articles as drafted and then "leaked" illustrate the difference between how the Justice Department and how politicians operate."That's not to say we're flawless," Rosenstein insisted. "But ... if we're going to accuse somebody of wrongdoing, we have to have admissible evidence, credible witnesses, we need to prove our case in court, and we have to affix our signature to the charging document. That's something that not everybody appreciates."He said many people concerned about secret government surveillance, approved by a federal judge under the Foreign Intelligence Surveillance Act , "seem not to recognize" that a FISA application is actually a warrant, "and in order to get a FISA search warrant" federal prosecutors need to present an affidavit and evidence, and it needs to be signed by a career federal law enforcement officer "who swears that the information in the affidavit is true and correct to the best of his knowledge and belief."If the information in the affidavit is found to be incorrect, the officer who signed it can face consequences, perhaps even prosecution, Rosenstein added."So that's the way we operate. We have people who are accountable," he said.Nevertheless, Rosenstein said that for "quite some time" now he has been threatened privately and publicly, "and I think they should understand by now the Department of Justice is not going to be extorted."Rosenstein has been publicly criticized by not only Republican lawmakers but also Trump himself.Just a few weeks ago, Trump tweeted that, "Much of the bad blood with Russia is caused by the Fake & Corrupt Russia Investigation, headed up by the all Democrat loyalists, or people that worked for Obama. Mueller is most conflicted of all (except Rosenstein who signed FISA & Comey letter)."On Tuesday, Rosenstein said the Justice Department is "going to do what is required by the rule of law ... and any kind of threats that anybody makes are not going to affect how we do our job.""We have a responsibility," and federal law enforcement officials swore an oath to defend the Constitution, he said.