In the 16 years since the Sept. 11 terror attacks, Donald Trump has evolved from a celebrity developer whose first public thoughts were about Manhattan's suddenly altered skyline to the combative commander in chief who warned "savage killers" on Monday "there is no dark corner beyond our reach."

Trump was in his Fifth Avenue penthouse that clear fall day in 2001, four miles from the World Trade Center and, seemingly, in a previous life from the one he now leads.

When the towers fell, he spoke with measured words about the attackers and about the wounds inflicted on his hometown, a sharp contrast to his more recent incendiary rhetoric about terrorists and his unproven claims about celebrating Muslims.

On Monday, his first 9/11 anniversary as president, Trump carried out a sadly familiar ritual for U.S. leaders.

He stood, head bowed and hands clasped, for a moment of silence at the White House to mark the instant that a hijacked airplane had slammed into the World Trade Center. Later, at the Pentagon, where another plane had crashed, he promised American resolve.

"'The terrorists who attacked us thought they could incite fear and weaken our spirit," Trump said. "But America cannot be intimidated, and those who try will join a long list of vanquished enemies who dared test our mettle."

"American forces are relentlessly pursuing and destroying the enemies of all civilized people," he declared. "We are making plain to these savage killers that there is no dark corner beyond our reach, no sanctuary beyond our grasp, and nowhere to hide anywhere on this very large Earth."

Trump's initial response in the hours after terror attacks was more restrained. He had flirted with a presidential run before, but he had yet to embrace some of the hardline ideas that later emerged in his campaign. Nor had he yet had his rebirth as a national celebrity thanks to "The Apprentice."

In a local radio interview, Trump said that if he were president he'd be taking "a very, very tough line" but he drew no conclusions about who perpetrated the assault on American soil.

"Most people feel they know at least approximately the group of people that did this and where they are," Trump told WWOR. "But, boy, would you have to take a hard line on this. This just can't be tolerated."

Trump vowed that his home city's spirit would not be broken. Nor his. He could not resist noting that with the destruction of the 110-story twin towers, his building at 40 Wall Street now stood above all others in Lower Manhattan.

"When they built the World Trade Center it became known as the second tallest," Trump said of his building. "And now it's the tallest."

In the years that followed, Trump's views on terrorism hardened and his claims about 9/11 grew more outlandish and untrue. As a candidate, he often pledged to "bomb the hell out of ISIS" and vowed to enact a Muslim ban.

In 2013, he posted a tweet saying, "I would like to extend my best wishes to all, even the haters and losers, on this special date, September 11th." And when his presidential campaign ramped up, he singled out Muslims in saying that "thousands of people were cheering" in Jersey City, New Jersey, across the Hudson River from lower Manhattan, as the towers collapsed. There is no such evidence in news archives.

Trump also said he lost "hundreds of friends" in the attack and helped clear rubble afterward. He has not provided the names of those he knew who perished in the attack, but has mentioned knowing a Roman Catholic priest who died while serving as a chaplain to the city's fire department.

He also criticized President George W. Bush, accusing him of failing in his duty to keep Americans safe. He repeatedly suggested President Barack Obama had not done enough to stamp out the threat posed by Islamic terror groups — in part by not clearly calling out the danger as "radical Islamic terror."

On Monday, neither Trump nor his top aides used that phrase, though Trump has said it since taking office.

The president has shown some signs of being affected by the gravity of his office. When he announced his war strategy for Afghanistan last month, he acknowledged that "decisions are much different when you sit behind the desk in the Oval Office." And on Monday, he took part in what has become a sobering annual tradition: Like Presidents Bush and Obama before him, he received a briefing on current terror concerns on the anniversary itself.

"The purpose of that is to give the president a sense of the terrorist threat globally and to the homeland," said Tom Bossert, Trump's homeland security adviser. Bossert said on this 9/11, there were no known active threats.

The briefing could mark another step in Trump's evolution, offering a fresh reminder that he now is the one most responsible for keeping the nation safe, according to James Clapper, who participated in the sessions as Obama's director of national intelligence.

"The focus in every one of our briefings, no matter the day, was to assess current threats and keep the nation safe," said Clapper. "But around Sept. 11 there was a sense of solemn obligation to those Americans who tragically died that day."

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Associated Press writers Darlene Superville and Ken Thomas contributed to this report.

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