Washington (CNN) President Donald Trump promised a new era guided by one principle -- "only America first" -- moments after being sworn in as the nation's 45th commander-in-chief.

But Friday's transfer of power from President Barack Obama's Democratic administration to Trump's nationalist Republican presidency featured many more symbolic moments from the former and new presidents and their families.

Here are memorable moments from Inauguration Day:

Trump takes the oath of office

At noon Friday, Trump placed his left hand on two Bibles -- one used by Abraham Lincoln in 1861 and one a gift from his mother when Trump graduated Sunday School in 1955 -- and pledged to preserve, protect and defend the Constitution.

With that, the nation had its 45th President.

JUST WATCHED Donald Trump sworn in as 45th US President Replay More Videos ... MUST WATCH Donald Trump sworn in as 45th US President 01:29

And then the rain came.

Trump stepped to the podium in front of a massive crowd of supporters -- though smaller than the throngs that attended President Barack Obama's inauguration in 2009 -- to deliver his inaugural address as raindrops splattered onto his shoulders.

Rev. Franklin Graham said after Trump's speech that "in the Bible, rain is a sign of God's blessing."

'The American carnage stops right here'

Trump stepped to the podium and delivered 16 minutes and 30 seconds of pure economic nationalism -- a revival of his campaign rhetoric and a rejection of much of Washington's hopes he might change once in office.

"This American carnage stops right here and stops right now," Trump said with Obama looking on.

"We assembled here today are issuing a new decree to be heard in every city, and in every foreign capital and in every hall of power," Trump said. "From this day forward, a new vision will govern our land. From this day forward, it's going to be only, 'America first! America first!'"

"Every decision on trade, on taxes, on immigration, on foreign affairs, will be made to benefit American workers and American families," Trump said.

JUST WATCHED Trump: America first and only America first Replay More Videos ... MUST WATCH Trump: America first and only America first 01:19

The philosophies Trump espoused weren't just a rejection of the former presidents -- particularly Bill Clinton, George W. Bush and Barack Obama -- sharing the stage with Trump. They threaten the conservative principles that are the bedrock of the Republican Party, too.

An hour later, Trump moved to the Capitol for a lunch with Congress -- the very same political class had just so sternly denounced.

The other transfer of power

The last time a new American president was inaugurated, Twitter wasn't the media powerhouse it is now.

So Trump's inauguration marked the first time the official @POTUS account had to be handed off.

At noon, Obama's tweets were all migrated to a new, archived account -- @POTUS44 -- and Trump took over the @POTUS account, which was suddenly empty.

For a few minutes, a president known for communicating directly with his supporters via Twitter had control of a massive account displaying an odd message for the prolific tweeter Trump: "@POTUS hasn't tweeted yet."

Hillary Clinton's nightmare

It was a split-screen for the ages: At the same moment Hillary and Bill Clinton descended the steps of the Capitol building, making their way to their seats in the audience, Obama and Trump left the White House to ride to inauguration together.

The two men who had denied former Secretary of State Clinton the presidency would arrive in the same car.

Clinton wore white -- a color with symbolism in the women's suffrage movement and her preference for major events, including her final debate with Trump and her speech accepting the Democratic nomination in Philadelphia.

JUST WATCHED Hillary Clinton arrives at Trump inauguration Replay More Videos ... MUST WATCH Hillary Clinton arrives at Trump inauguration 00:56

Before Trump's inauguration, Clinton's official account posted a tweet about her presence: "I'm here today to honor our democracy & its enduring values. I will never stop believing in our country & its future."

She was composed throughout the ceremony, but Friday was the day she had warned supporters about.

"Imagine that on January 20, 2017, it is Donald Trump standing in front of our Capitol and taking the oath of office," Clinton had said in a dire warning to supporters in Las Vegas, just three days from the election. "Imagine with me what it would be like to have Donald Trump sitting in the Oval Office come next January."

But later, Trump honors Clinton

While Trump made no mention of Hillary Clinton in his inaugural address he did single her out during the Capitol luncheon afterward, saying he was honored the Clintons were in attendance.

"I'd like you to stand up," Trump said to Hillary Clinton.

The entire room stood, turned to the Clintons and applauded, as Trump gave the rival he once promised to jail a finger-point and a thumbs-up.

"And honestly, there's nothing more I can say, because I have a lot of respect for those two people," Trump said of the Clintons.

Trump kept his remarks short, thanking congressional leaders for a photograph of his inauguration that was presented and nodding toward bipartisan cooperation.

"We're all dealing together, we all want the same thing, we're all good people," Trump said. "Whether you're a Republican or Democrat, it doesn't make any difference."

The Trumps and Obamas meet

Barack and Michelle Obama were waiting at the White House steps to greet Donald and Melania Trump Friday morning after the Trumps attended church across from Lafayette Square.

The moment was of symbolic importance, showing the willful and peaceful transfer of power.

But it also showed just how awkward it can be to greet new acquaintances with the entire world watching.

As Melania Trump went extended her hand for a shake, Michelle Obama leaned in, saying, "I'm a hugger" -- prompting Barack Obama to joke about the "protocol" for such occasions.

JUST WATCHED The Obamas greet the Trumps at White House Replay More Videos ... MUST WATCH The Obamas greet the Trumps at White House 01:05

The Trumps also brought a large, flat gift box from Tiffany and Co. -- which the outgoing President had to stash in the White House before the four could pose for a round of photos on the White House steps.

Michelle Obama's sadness

The Obamas and Trumps were together again after Trump's inaugural address, as the Obamas prepared to depart via helicopter for Joint Base Andrews for a family vacation in Palm Springs, California.

Walking down the back steps of the Capitol, Trump leaned into Obama and uttered something -- far enough away that microphones didn't pick it up -- that caused Obama to laugh.

The former and new presidents talked and joked as the Pences and Bidens said their goodbyes.

But the look on Michelle Obama's face was much different -- and seemed to reflect sadness.

It's impossible to know what was in her mind. But it was, after all, Michelle Obama who delivered the strongest rebukes of Trump on the campaign trail for Clinton. And Trump's inaugural address had been a complete repudiation of Obama's presidency and political vision.

As the Star-Spangled Banner played at Joint Base Andrews, Barack and Michelle Obama stood, singing, with tears in their eyes -- their last public moment on the last day of the Obama presidency.

Trump the pen dispenser

Trump sat down at Capitol Hill to take his first official actions as President: Signing a waiver allowing former Gen. James Mattis to become secretary of defense; a proclamation of a national day of patriotism; and nominations for his Cabinet.

Huddled around him were his family and the top-ranking members of Congress -- and Trump immediately began schmoozing, handing out the pens he used to sign the nominations.

"I got Price," said House Minority leader Nancy Pelosi, referring to Trump's nominee for Health and Human Services secretary.

"You want Elaine's?" Trump asked Pelosi. That is Elaine Chao, Trump's transportation secretary pick, who is also the wife of Senate Majority Leader Mitch McConnell -- who was standing nearby.

"Here's one I think Nancy would like ... Scott Pruitt," Trump joked. Pruitt, Trump's EPA pick, is opposed by liberals.

As the lawmakers laughed, Trump's family was less impressed. Son Barron, 10, stood over Trump's shoulder, playing peek-a-boo with older half-sister Ivanka Trump's baby.

Trump's parade

As the inaugural parade wound its way toward the White House, Trump, wife Melania and son Barron all exited the presidential limousine and walked, waving to the adoring crowds.

Trump didn't actually walk past the Trump International Hotel -- his business's new location along the parade route. He got back into the limousine about half a block before reaching it.

Later, Trump got back out of the limo in front of the Treasury Department to wave to crowds again.

Protesters downtown

Just blocks from Trump's inaugural parade, protesters were clashing with police.

A limo was on fire. Windows to a Starbucks and several other businesses had been smashed. Police were using pepper spray to control protesters who were destroying property.

Two police officers suffered minor injuries in clashes with the protesters, and 95 had been arrested by mid-afternoon.