"Nobody wants to get off on the wrong foot with the new boss. We're heading into this different era where it's hostile," one official said.
Another official added, "It's a sad day when politicians place more stock in (Russian President Vladimir Putin and (WikiLeaks founder) Julian Assange than in the Americans who risk their lives daily to provide objective, non-partisan intelligence analysis."
That was a reference to Trump's tweet on Wednesday noting that Assange said he didn't get hacked Democratic Party emails from the Russians
, who have also denied the hacking allegations.
Adding to the concern, officials said there is a disconnect between Trump's public pronouncements about the intelligence community
and his behind-the-scenes behavior when he's sitting across the table at closed-door intel briefings.
US officials familiar with the briefings said Trump is for the most part professional, deferential and polite. He listens but does not engage frequently during the briefings, other officials said, although at times he has challenged and questioned information.
A senior transition source told CNN that Trump does ask questions, adding, "Questions are good." The transition official said the President-elect does not question the data presented to him but he does question some of the conclusions drawn from the data.
US officials said the alleged election hacks and Russia have come up in briefings with Trump, but the full picture of what all the different intelligence threads mean has not been presented to him yet. That will happen during a briefing that is scheduled Friday with leaders of the intelligence community.
As officials try to make sense of Trump's skepticism, one theory is that the President-elect is acting out because he believes that the intelligence community is trying to undermine his victory with information that Russia tried to affect the 2016 vote.
"The intelligence community is not saying that Vladimir Putin won the election for Trump," the official said. "We're saying they did a series of things to sow doubt and some people think they wanted Trump to win, but no one has ever said they got into the mechanics of the ballot boxes."