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Maybe it's the power of the Oval Office.

The day after President Donald Trump's joint address to Congress, a White House official credited the widely noted shift in the president's tone to the responsibility he feels now that he’s been in office for several weeks and the optimism he harbors for the country.

Trump embraced an Oval Office approach in Tuesday night's address on Capitol Hill, a stark reversal for a candidate known for careening off script and often ad-libbing newsworthy comments that trampled on his core message. The speech repackaged Trump’s “America First” message with rosier-than-usual shine, despite few substantive changes to the kinds of broad policy prescriptions Trump has advocated all along.

President Donald Trump points after delivering his first address to a joint session of Congress on Tuesday night. Jim Lo Scalzo / Pool via EPA

On display was a side of the president long talked about by friends and advisers who know him well, but is not often seen by the public. Trump added characteristic flourishes of “very” and emphasized figures like trillion or billion by repeating them when they appeared in his remarks, but communicated his vision with a calmer tone than the one he used to rally his supporters on the campaign trail.

Attacks on his perceived enemies were largely absent.

Related: Black Congressional leaders react to Trump address

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The stakes and the setting also played a role in Tuesday night’s calculus. Trump has a reputation among advisers and friends for knowing how to read a room — and it showed.

"The president makes the decision to set the tone he wants," an official familiar with the speech-writing process told NBC News.

Multiple officials also credited Trump with the bulk of the remarks.

He personally edited each draft of the speech, which White House Press Secretary Sean Spicer told reporters was “from his heart,” while soliciting input from advisers and family members, among them son-in-law Jared Kushner, daughter Ivanka Trump, Chief of Staff Reince Priebus, Chief Economic Adviser Gary Cohn, Chief Strategist Stephen Bannon, Kellyanne Conway, and longtime speechwriter Stephen Miller.

Vice President Mike Pence called the speech “all” Trump on Wednesday morning and said it showed the president’s willingness to “make his case and challenge his detractors when unfair criticism comes his way.”

But some critics, like immigration activist Astrid Silva, said the speech “sounded the exact same as when he was on the campaign trail, just in a much calmer tone.”

Throughout the 2016 campaign, those following his campaign openly wondered when, if ever, Trump’s pivot would come. With each new campaign regime change came the familiar question: would this finally bring an impetus for change in the candidate's behavior?

But Trump never truly abandoned the public settling of scores from the stump that earned him notoriety early in the primary process, even after he began to use TelePrompters at the urging of his aides. Though he often eclipsed his core message of jobs, national security, and the need for change in Washington, voters still appreciated his off-the-cuff, say anything style.

Related: The president's softer tone

On Wednesday, the White House was jubilant.

One staffer told NBC News the overall feeling during the speech was “very, very proud.” Wednesday was a “very” happy day at the White House, the staffer said.

Though the president’s famous Twitter feed was mostly quiet — he did tweet an all-caps "THANK YOU!" just before 9am Wednesday — several staffers took to their boss’ social media platform of choice to applaud the speech.

PHOTOS: Scenes from Trump's Address

White House Deputy Press Secretary Sarah Huckabee Sanders called it a “truly incredible night.” Another deputy in the communications shop, Linsday Walters, tweeted that it was “a display of true leadership.” Other staffers retweeted reactions from members of the media, people previously called enemies of the American people by the president, who had nice things to say about the address.

Possibly sensing a PR tide turning in their favor, the White House postponed the foreshadowed roll out of the latest iteration of the president’s controversial travel ban. A senior administration official told NBC News late Tuesday night that they wanted to let the joint address breath.