WASHINGTON (Reuters) – Overwhelmed during the deadly attack on Congress by President Donald Trump's supporters last week, U.S. security forces are mounting a national operation to thwart any violence before President-elect Joe Biden takes office. Federal and state officials are evaluating online threats and menacing messages to members of Congress and making sure the security operation has the force to repel an attack. The incoming Biden administration has significantly ramped up security around his team ahead of the Jan. 20 inauguration. One police officer and four protesters died in the siege, which began after Trump called on thousands of supporters to march on Congress in a bid to stop the final certification of Biden's election victory.