Trump campaign spokesperson Tim Murtaugh says the campaign is working with law enforcement authorities to investigate the source of what it called an "attack."
He adds, "There was no exposure to sensitive data because none of it is actually stored on the site."
A screenshot of the site shows that it briefly displayed a warning claiming that it had been "seized" because "the world has had enough of the fake-news spreaded daily by president donald j trump."
WATCH | President Trump delivers remarks at Robeson County Fairgrounds
President Donald Trump delivers remarks at Robeson County Fairgrounds on Saturday
It later displayed an error message that read, in part, "This site is currently offline."
The website has since been restored.
The FBI did not immediately respond to a message seeking comment.