Washington (CNN) With the Republican and Democratic nominees officially in place, White House officials are beginning their efforts to prepare both Donald Trump and Hillary Clinton to assume office in January.

White House Chief of Staff Denis McDonough phoned the Trump and Clinton transition teams Friday to invite them for preparation sessions on the complex workings of the federal government. It's the latest step in a process that began months ago to ensure a smooth transfer of power next January, no matter who wins.

In his phone calls, McDonough also advised both teams their candidates are now eligible for classified intelligence briefings, administered by the Director of National Intelligence. Opponents of both candidates have claimed neither Trump nor Clinton should be trusted with sensitive information.

McDonough spoke with Gov. Chris Christie of New Jersey, who is heading Trump's transition team, and Ed Meier, who is completing that task for Clinton.

"The peaceful transfer of power is a bedrock principle of our democracy, and the President has made clear that a smooth transition between administrations is one of his top priorities," said Brandi Hoffine, a White House spokeswoman.

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