According to a pool report, Moore showed up at the 58-story skyscraper in midtown Manhattan this afternoon and walked into the building, which is open to the public. He had a safety pin fastened to his clothing -- a gesture some people are taking to show solidarity for minority groups that have been maligned by Trump.
As he toured the landmark Fifth Avenue skyscraper with a slew of reporters, Moore said Trump "does not have the vote of the people" because claimed victory in the electoral college but did not win the popular vote.
"I didn't think I'd get this far," he told reporters as he headed up to the third floor.
Moore was stopped by security on the fourth floor. When he asked for a meeting with Trump, a Secret Service agent replied: "You'd have to check with his staff."
Trump Tower is normally open to the public, and security checks bags as visors enter. But now that Trump is the president-elect, Trump Tower has become like a fortress, surrounded by police officers, metal barricades, checkpoints and street closings. The heightened security measures are a team effort by the Secret Service, the New York Police Department and Trump's own private security personnel.
On Thursday, the Federal Aviation Administration on Thursday established a no-fly zone, effective immediately, over midtown Manhattan until Jan. 21, 2017, the day after Trump is scheduled to be inaugurated as the 45th president of the United States. The FAA's order cites "VIP movement" as the reason.
ABC News' Jeffrey Cook contributed to this report. The Associated Press also contributed to this report.