Thousands of military personnel guarding Joe Biden’s inauguration as US president on Wednesday are being vetted by the FBI amid fears of an insider attack. The biggest ever security operation for a presidential transition has turned swaths of Washington into a fortress, barricades, razor wire and 7ft fences erected to prevent a repeat of the deadly 6 January attack on the US Capitol by a mob incited by Donald Trump. National guard personnel train part-time while holding civilian jobs or attending college. Some 25,000 members – more than double the number at previous inaugurations – are pouring into Washington from across the country, at short notice. There are concerns that some of the very people assigned to protect the city could present a threat to the incoming president and other dignitaries, the Associated Press reported. Their names will be fed through an FBI database for any evidence of connections to investigations or terrorism or other red flags. Ryan McCarthy, the army secretary, told the AP guard members were receiving training on how to identify potential insider threats, although no hard evidence had come to light. “We’re continually going through the process, and taking second, third looks at every one of the individuals assigned to this operation,” he said, adding: “We need to be conscious of it and we need to put all of the mechanisms in place to thoroughly vet these men and women who would support any operations like this.” At least two active-duty service members or national guard members have been arrested in connection with the Capitol assault. Video footage from inside the building suggests some rioters had military training and that there was a significant level of planning and coordination. The Pentagon received 143 notifications of extremism-related investigation last year from the FBI, 68 of which were related to current and former service members, the Washington Post reported. The national guard played down fears of extremism in its ranks. Maj Gen William Walker, commanding general of the DC national guard, told MSNBC: “I don’t have any concerns because it’s a layered scrub. The FBI is scrubbing, the Secret Service gives out the credentials and then we have other agencies helping with the scrub as well. We really are pretty sure we know who is out here supporting us.” But Washington remains on edge amid fears of attacks by far-right militants, white supremacists and other radical groups encouraged by Trump’s claims that the election was rigged – claims repeatedly tossed out of court and rejected by the US Department of Justice and Republican election officials in battleground states. Five people including a Capitol police officer died in the mayhem on 6 January, which included chants for the death of Vice-President Mike Pence as he presided over the certification of Biden’s victory. Pence will attend the inauguration, with former presidents Bill Clinton, George W Bush and Barack Obama and their wives. Lady Gaga and Jennifer Lopez will be among the performers. Attendance will be scaled down because of the coronavirus pandemic. The Secret Service is in charge of security but a wide variety of military and law enforcement personnel are also involved, from the national guard and FBI to three police departments. The Capitol was temporarily closed on Monday after a fire broke out at a homeless encampment, Capitol police said. All participants in a rehearsal for the inauguration were evacuated into the building, Reuters reported, before the Secret Service said there was no threat to the public. State capitols across the US stayed on alert. Weekend protests were calm and thinly attended but some pro-Trump demonstrators carried weapons. On Monday Andrew Cuomo, the Democratic governor of New York, said he would skip the inauguration to guard against the possibility of violence in his state capital, Albany. On Monday – a public holiday celebrating the birthday of Martin Luther King – Trump remained behind closed doors at a mostly deserted White House. Biden, wearing black cap, dark glasses, black mask and blue and yellow gloves, stood at a conveyor belt packing beans and rice for a food bank in Philadelphia. Trump was reportedly planning to issue more than 100 pardons as his last major act in office. The president met his son-in-law Jared Kushner, daughter Ivanka Trump and senior advisers on Sunday to thrash out a lengthy list of requests, the Post reported. Trump will be the first outgoing president to skip his successor’s swearing-in since Andrew Johnson did not attend the inauguration of Ulysses S Grant in 1869. Johnson, like Clinton, was impeached. Trump is the only president to be impeached twice. Trump has requested a departure ceremony at Joint Base Andrews with a military band and red carpet, ABC News reported. He will then head to his luxury estate, Mar-a-Lago, in West Palm Beach, Florida, to begin an uncertain future. Impeached by the House of Representatives for inciting violence against the US government, he is awaiting a trial in the Senate and a potential ban from running for office. By the time Biden takes the stage on Wednesday, the death toll from coronavirus in the US will in all likelihood have passed 400,000. The pandemic is among “four crises” identified by the new president – along with the economy, climate change and racial injustice. Biden is set to hit the ground running by reversing many of Trump’s most contentious policies with a flurry of executive orders, returning the US to the Paris climate agreement and Iran nuclear deal, accelerating the delivery of Covid-19 vaccines and canceling an immigration ban on some Muslim-majority countries. Kamala Harris, the vice-president-elect, resigned her Senate seat on Monday. She will be replaced by the California secretary of state, Alex Padilla.