WASHINGTON - The newly appointed second-in-command at the US Justice Department faced a weighty task just two weeks after taking office - writing the rationale for firing FBI Director James Comey.US Deputy Attorney General Rod Rosenstein argued the case for Comey's sacking in a three-page memo to Attorney General Jeff Sessions on Tuesday. President Donald Trump acted swiftly to dismiss the director later that day. Rosenstein cited Comey's controversial public statements about the bureau's investigation into Democratic presidential candidate Hillary Clinton's use of a private email server while she was secretary of state."It is a textbook example of what federal prosecutors and agents are taught not to do," Rosenstein wrote of Comey's public comments.Spokespeople for the Department of Justice and the FBI did not return calls seeking comment late Tuesday.Comey's firing will likely be seen as further evidence of Washington's hyper-partisan upheaval. Rosenstein has drawn fire from Democrats who allege political motives in the White House decision to dismiss Comey - and particularly, its timing."Why did it happen today?" asked Senate Democratic Minority Leader Chuck Schumer, of New York. "We know the FBI has been looking into whether the Trump campaign colluded with the Russians ... Were those investigations getting too close to home for the President?"The rationale for canning Comey, however, came from a 26-year Justice Department veteran who is widely viewed by his peers and many lawmakers as uncommonly nonpartisan.Named as Maryland’s top prosecutor by President George W. Bush, Rosenstein stayed in office through the Obama administration.Rosenstein was the longest-serving US attorney when he was nominated by Trump last January.When he was confirmed by the Senate, he enjoyed overwhelming bipartisan support - a 94-to-6 vote - despite the deeply divided culture of today's Washington.Bonnie Greenberg, a federal prosecutor in Maryland told Reuters in March that Rosenstein was admired as a rare career prosecutor who could insulate himself from political pressure."He only does something if he thinks it's right," said Greenberg, who worked with Rosenstein for 11 years.Many in the Justice Department saw Rosenstein's appointment as a counter-balance to the extreme partisanship surrounding accusations of Russian interference in last year's election. And he was immediately swept into that fray.Before Rosenstein was confirmed for the position by the US Senate, some Democratic lawmakers asked him to pledge he would appoint a special independent prosecutor to investigate allegations of collusion between the Trump campaign and Russian officials.He was easily confirmed despite rebuffing those demands.