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 in the pre-election period, including identifying agency review teams and beginning the background check process for national security staff.

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. It is not clear why Trump, who sewed up the nomination months ago, did not start sooner.

Max Stier, 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.

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.

Trump has brought former Democratic Rep. Tulsi Gabbard and independent presidential candidate Robert F. Kennedy Jr. onto his transition team, Brian Hughes, a senior adviser to the Trump campaign, confirmed Tuesday.

Kennedy ended his independent campaign for president and endorsed Trump on Friday.

Gabbard, a former member of Congress who represented Hawaii and left the Democratic Party after her 2020 presidential run, endorsed Trump on Monday and has been helping him with debate preparation in recent weeks.

It’s unclear what exactly she and Kennedy will do in their transition roles, but they will join Trump’s sons, Donald Trump Jr. and Eric Trump, as well as his running mate, Sen. JD Vance, R-Ohio, as honorary chairs of the transition team.

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 hand-off, including misplaced expectations about continuity between presidents and the risk of hubris in those who’ve served in government recently assuming more significant roles.

Former Small Business Administrator Linda McMahon and billionaire Howard Lutnick will lead Trump’s transition team.

Harris 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 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.

“We look forward to this notification and will reply when we have evaluated what is being offered, Hughes said.

GSA is required by law to make available federal office space, IT support and other resources to transition teams starting Tuesday, but only once it has entered into memoranda of understanding with representatives for each nominee, which Congress requires the agency to do “to the maximum extent practicable,” by Sept. 1. A GSA spokesperson confirmed that the agency had made its offer to the two candidates Tuesday.

“Both teams will really want to have the infrastructure set up behind the scenes that allows them to conduct meetings with federal agencies and manage a resume bank, and have an organized process for all of the personnel and policy planning confronting them should they win the election,” said Valerie Smith Boyd, director of the Partnership for Public Service’s Center for Presidential Transition.

The New York Times contributed.