WASHINGTON — The Biden administration offered federal resources to Donald Trump and Kamala Harris for presidential transition planning for the first time Tuesday, with experts suggesting both are behind in preparing for their potential administrations.

While transitions kick into high gear after Election Day, when a president-elect must begin selecting and vetting about 4,000 federal political appointees, success depends on the infrastructure built during the pre-election period, including identifying agency review teams and beginning the background check process for national security staff.

Both Vice President Harris and former President Trump started the process this month, months later than prior transitions. Harris was elevated to the top of the Democratic ticket just five weeks ago after President Joe Biden dropped his reelection bid, and she had to first redirect his political operation before laying the groundwork for the transition. It is not clear why Trump, who sewed up the nomination months ago, did not start sooner.

Max Stier, the president and CEO of the Partnership for Public Service, said planning to take office in the modern era has tended to begin in the late spring.

“It is possible to try and catch up, but the reality is that both candidates have a lot to do,” he said.

Tuesday is the congressionally mandated date for the General Services Administration to make space available for Trump and Harris, three business days after the second nominating convention. The office space is just blocks from the White House, with even more federal resources set to flow to the winner after Election Day. But nominees usually start the initial planning for their potential administrations soon after they lock up the nomination, even before they begin receiving federal support.

Harris, if she wins, may choose to keep some political appointees from the Biden administration — potentially helping her avoid messy confirmation fights if Republicans take control of the Senate. But significant change is inevitable, as she will want to put her own stamp on government. And many long-serving Biden administration officials are likely seeking to exit for other opportunities regardless of the outcome in November.

Trump, meanwhile, is likely to try to avoid mistakes of his 2016 transition, when he shelved months of planning by a group led by former New Jersey Gov. Chris Christie. That left Trump and his team, many of whom had never served in government, unprepared after Election Day.

Stier said Trump’s 2016 effort set a low bar for transition efforts in the modern era, followed by George H.W. Bush’s 1988 effort as the then-vice president prepared to take over from President Ronald Reagan. He said there can be a special challenge in negotiating a same-party handoff, including misplaced expectations about continuity between presidents and the risk of hubris in those who’ve served in government recently assuming more significant roles.

Trump formally stood up his transition team earlier this month to be led by former Small Business Administrator Linda McMahon and billionaire Howard Lutnick.

Harris has asked Yohannes Abraham, the ambassador to the Association of Southeast Asian Nations and the executive director of the Biden-Harris 2020 transition, to lead her planning for the White House.

Abraham is set to leave his position in the coming days to assume the role. Covington & Burling, LLP, which assisted Harris in vetting her vice presidential pick, will provide legal counsel to the transition organization.

According to a person familiar with the planning, Harris’ transition team won’t make any personnel decisions before the election, nor will it develop policy — functions that will remain with Harris’ campaign and official office.

Trump’s team, meanwhile, has not committed to accepting the federal support. Trump told the Daily Mail last week that he would decline access to traditional pre-Election Day intelligence briefings, saying he was worried about being accused of leaking classified information.