White House Chief of Staff John Kelly attends a Cabinet Meeting in the Cabinet Room of the White House on August 16, 2018 in Washington, DC.Getty ImagesPresident Donald Trump’s delay in starting the transition of power to President-elect Joe Biden is hurting U.S. national security, his former chief of staff John Kelly told Politico on Friday.”You lose a lot if the transition is delayed because the new people are not allowed to get their head in the game,” Kelly said. “The president, with all due respect, does not have to concede. But it’s about the nation.””It hurts our national security because the people who should be getting [up to speed], it’s not a process where you go from zero to 1,000 miles per hour.”Kelly said Biden should start receiving intelligence briefings, Politico reported.Kelly’s comments come as Biden advisors grow increasingly concerned about the president-elect’s lack of briefings on national security and on the federal coronavirus response.Republican Sen. Chuck Grassley on Thursday said Biden should be receiving classified intelligence briefings from the Trump administration.General Services Administration chief Emily Murphy has yet to perform the customary duty of ascertaining that Biden had indeed won the race. NBC and other major news outlets projected Biden secured the presidency Saturday.”The Trump Administration is following all statutory requirements,” White House spokesperson Judd Deere said in an email.Trump has refused to concede the race, claiming the election was “rigged” even as there has been no evidence of widespread voter fraud.His campaign is mounting multiple legal challenges in swing states in an effort to reverse election outcomes. Attempts in Arizona, Michigan and Pennsylvania have already been dropped or denied.