Devoted Aide Who Keeps Good News Flowing Will Follow Trump to the White House

President-elect Donald J. Trump has always demanded loyalty from his aides, but few have answered the call quite like Natalie Harp.

A 33-year-old former far-right cable host, Ms. Harp is nearly always at Mr. Trump’s side. She has written him a series of devotional letters, including one that said, “You are all that matters to me.” Once, when Mr. Trump was playing golf in Scotland, she ran behind his cart to keep him up to date with positive stories and social media posts.

Little known beyond Mr. Trump’s immediate orbit, Ms. Harp is now poised to play a potentially influential role in his White House, sitting right outside the Oval Office and acting as the conduit for a largely unsupervised flow of information to and from the president and helping him with his social media feed.

She has no official title, but during the campaign, colleagues referred to her as the “human printer” because she followed Mr. Trump around with a portable printer and a battery pack to charge it, so she could hand him information in hard copy, as he prefers.

But Ms. Harp also established herself at the center of a fast-moving carousel of text messages, articles and tidbits directed at Mr. Trump. This has generated concern among other aides who feel she has been far too willing to serve as a funnel for conspiratorial information at a moment when Mr. Trump appears more contemptuous than ever of attempts to manage or control him. One of her go-to news sources, people who have observed her say, is the website Gateway Pundit, which frequently disseminates conspiracy theories embraced by the far right.