Certain staffers in the FBI's New York Field Office have been told to expect a special guest tomorrow: Donald Trump.
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He is scheduled to receive his first classified briefing as the Republican Party's presidential nominee, according to sources notified of the upcoming visit.
Trump is planning to take with him New Jersey Gov. Chris Christie and retired Lt. Gen. Michael Flynn, a former Defense Intelligence Agency director who has become an outspoken supporter of Trump, a senior campaign official said.
Career staffers from the Office of the Director of National Intelligence (DNI), the nation's top intelligence office, will be leading the briefing, which is expected to cover major threats and emerging concerns around the world.
Trump's session comes two days after he laid out a series of foreign policy proposals, including plans for subjecting immigrants to "extreme vetting" and temporarily blocking immigration from "the most dangerous and volatile regions of the world."
Because of the sensitivity of the information discussed during briefings of presidential candidates, the sessions must take place in locations with secure rooms, known as sensitive compartmented information facilities. The FBI's office in New York City has such rooms.
The FBI, however, will have no role in the briefing beyond playing host, ABC News was told.
The decision to take Christie and Flynn with him could stoke speculation that Trump is considering them for positions in his Cabinet.
Both spoke in support of Trump at the Republican National Convention in Cleveland last month. And – unlike Trump – both would have had to receive security clearances to attend the briefing.
As a U.S. attorney under George W. Bush's administration, Christie ran the federal prosecutors' office in New Jersey for several years, and he is now leading Trump's transition team.
In 2014, Flynn retired as the head of the Defense Intelligence Agency after a long career in military service. He has recently received criticism for some of his public positions, including a retweet of an anti-Semitic message and the posting of a tweet that read, "Fear of Muslims is RATIONAL."
As for Trump, many of his critics, including top Democratic senators, have questioned whether he is fit to receive classified information, citing controversial statements he has made on the campaign trail.
But DNI Director James Clapper and the White House recently said they have no qualms about briefing the Republican or Democratic presidential candidates, noting that providing the briefings is a "long-standing tradition in our system," dating back more than 60 years.
"Ensuring a smooth transition to the next president is a top priority ... and that's important, in part, because of the significant threats around the world," White House spokesman Josh Earnest told reporters in Washington, D.C., last month.
He said U.S. intelligence officials "understand what steps are necessary to protect sensitive national security information, and the administration is confident that they can both provide relevant and sufficient briefings to the two major-party presidential candidates while also protecting sensitive national security information."
Clapper said there is no concern in the U.S. intelligence community about providing classified information to either of the presidential candidates, insisting, "It's not up to the administration and certainly not up to me personally to decide on the suitability of a presidential candidate."
"The American electorate is in the process of deciding the suitability of these two candidates to serve as commander in chief, and they will make that decision, to pick someone who will be cleared for everything," Clapper said at the annual Aspen Security Forum in Colorado last month.
Each of the campaigns decides the location for the classified briefings, according to Clapper.
Trump and Democratic nominee Hillary Clinton are each expected to receive two or three classified briefings before Election Day.
These briefings resemble the annual Worldwide Threat Assessment issued by the intelligence community, which releases an unclassified version each year. While some top-secret information could be discussed, the briefings will not include the nation's most sensitive secrets, particularly information on sources, methods and operations.
Trump began this week with a campaign rally in Youngstown, Ohio, where he laid out his plan to fight "radical Islamic terrorism" and "make America safe again."
He proposed subjecting immigrants who want to enter the United States to "extreme vetting" and a new ideological test, saying it would help ensure that only "those who share our values and respect our people" are admitted into the country.
--ABC News' Veronica Stracqualursi, Justin Fishel, Alex Mallin and Devin Dwyer contributed to this report.