The Post’s Marc Fisher explains how some of President-elect Donald Trump’s traits could inform his leadership style when he takes office. (Bastien Inzaurralde/The Washington Post)

The Post’s Marc Fisher explains how some of President-elect Donald Trump’s traits could inform his leadership style when he takes office. (Bastien Inzaurralde/The Washington Post)

Washington began its transition of power Wednesday as the ascendancy of President-elect Donald Trump promised a seismic shift in nearly every facet of the capital city, from military and executive agencies to federal courts and financial and political establishments.

President Obama, who had denounced Trump as unfit to serve as commander in chief, struck a conciliatory note in the Rose Garden of the White House, vowing to work with his successor to ensure a peaceful transfer. The two men, who spoke by phone early Wednesday morning, plan to meet Thursday.

Claiming an electoral mandate after maintaining majorities in both chambers of Congress, Trump’s resurgent Republican Party planned an aggressive and sweeping program to systematically dismantle Obama’s policies and to usher in a new era of conservative governance.

For the GOP, there were signs of unity after a season of acrimony brought by Trump’s divisive candidacy, which antagonized party leaders.

House Speaker Paul D. Ryan (R-Wis.), who had all but abandoned the presidential nominee in the final weeks of the campaign, pledged that he and Trump would “work hand-in-hand on a positive agenda to tackle this country’s big challenges.”

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“Now is the time to shake the Earth,” said William J. Bennett, a Trump ally and former education secretary in Ronald Reagan’s Cabinet. “Anything is possible.”

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Senate Majority Leader Mitch McConnell (R-Ky.) said that Trump could “unilaterally” unravel Obama’s legacy early next year — starting with the Affordable Care Act, the president’s signature health-care accomplishment.

But, McConnell said, “I think it’s always a mistake to misread your mandate, and frequently new majorities think it’s going to be forever. Nothing is forever in this country. . . . We’ve been given a temporary lease on power, if you will. And I think we need to use it responsibly.”

One key relationship for Trump could be the one with Sen. Charles E. Schumer, who is expected to become the Senate Democratic leader in January.

“Is he going to reach out to build a Trump majority which will include Democrats, whether it’s in the Cabinet or the essential relationship with Schumer, who he’s known for many, many years?” asked former House speaker Newt Gingrich, an adviser to Trump and a potential appointee in the new administration.

“He is positioned to be the president of a very large coalition — and that coalition is bigger than the Republican Party,” he continued. “He has to think through, ‘How do you operationalize that at a practical level that works?’ ”

Trump called Schumer on Wednesday and the senator congratulated him. “It is time for the country to come together and heal the bitter wounds from the campaign,” Schumer said in a statement.

In New York, Trump confronted the urgent task not only of uniting a fractured nation but also of forming a government. The celebrity businessman, who has never before held public office, met at Trump Tower with Vice President-elect Mike Pence and their advisers and contemplated the makeup of his White House and Cabinet, as well as what he would do following his Jan. 20 inauguration.

A transition team chaired by New Jersey Gov. Chris Christie (R) has been working in Washington since the summer to lay the groundwork for a Trump administration. The group has been run by Rich Bagger, a longtime Christie adviser; William Hagerty, a key player on 2012 GOP nominee Mitt Romney’s transition team; and other establishment hands.

Michael O. Leavitt, a former Utah governor and health secretary in President George W. Bush’s Cabinet who was Romney’s transition chairman, has been informally advising the Trump team.

Something Trump must contemplate is how transformative his initial plans might be.

“Does he want to recruit people to manage the federal government or to change the federal government?” Gingrich said. “They’re very different job descriptions . . . Do you go out and recruit people who’ve turned companies around and not just people who’ve managed companies? And do you set goals and metrics for them as change agents?”

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Throughout his insurgent campaign, Trump has relied on a tight-knit cadre of aides and associates and has valued their loyalty above all else. Many of them are expected to join him in Washington.

Two leading candidates for White House chief of staff are believed to be Reince Priebus, the Republican National Committee chairman, and Corey Lewandowski, Trump’s first campaign manager who is now a paid commentator for CNN, according to two people familiar with the deliberations who requested anonymity because the talks are private.

Both Priebus and Lewandow­ski were at Trump Tower on Wednesday, as were RNC chief strategist Sean Spicer, policy adviser Stephen Miller, campaign chief executive Stephen K. Bannon and other advisers.

Priebus and Lewandowski would bring different attributes to the job. As party chairman for nearly six years, Priebus boasts deep ties with the GOP’s elected officials, donors and other luminaries, as well as a long friendship and shared Wisconsin roots with Ryan, which could prove helpful in managing relationships at both ends of Pennsylvania Avenue.

Lewandowski would be a relative newcomer to the Washington power structure but has the trust and confidence of the president-elect, having mapped out the strategy for his improbable campaign and executed it during the primaries. Trump fired Lewandowski in June, though they have remained close, and Lewandowski is credited with helping guide Trump’s general-election campaign in New Hampshire.

“Corey Lewandowski is trying very, very hard to become the chief of staff,” said one Republican familiar with the talks about Trump’s appointments. “He’s been talking about it for months, preparing for months and lining up all the right people to get it done. . . . Corey is saying it’s about loyalty. Nobody is more loyal.”

Trump’s orbit was abuzz Wednesday with speculation about which other loyalists might land jobs in the new administration.

Would Kellyanne Conway, a longtime pollster and communications guru who managed Trump’s campaign in the closing months and became a calming influence on the often-undisciplined candidate, be at his side in the West Wing?

Who would be the face of the White House in the press secretary role? Boris Epshteyn, a Trump surrogate who appeared frequently on cable television and anchored the campaign’s Facebook Live broadcasts? Jason Miller, the campaign’s senior communications adviser? Or Spicer, a more familiar face for the Washington press corps?

[Many of Trump’s sweeping promises will be hard, if not impossible, to fulfill]

Where might Christie land, after risking his political reputation to become in February one of the first establishment figures to endorse Trump? And would his connection to the bridge-closing scandal, in which two of his former aides were recently convicted, stymie his chances at Senate confirmation for Cabinet posts such as attorney general or secretary of state?

Former New Jersey governor Thomas H. Kean (R), who has known Christie for decades, said Christie was certain to end up somewhere in the administration “because Trump values loyalty more than anything.”

William M. Daley, a former Obama White House chief of staff, said Trump should move slowly with making appointments and thoroughly vet his nominees. “Stumbles can be devastating and convey not being ready for prime time, which will be something they should be sensitive to,” he said.

Daley counseled the president-elect’s team to “say little and act in a deliberate way,” adding that the new administration must show that it is seasoned and can be trusted to handle a crisis. He noted Trump’s poor approval ratings and the fact that Clinton beat him in the national popular vote, despite losing in the electoral college.

“People will watch to see whether the new administration acts as though it has a mandate or looks at the fact that more people voted against him than for him as a brake on those who want revenge or want to jam ideas onto a skeptical people,” Daley said.

Kenneth M. Duberstein, a former White House chief of staff to Reagan, said: “Twenty-four hours ago, you and others were writing that Hillary’s campaign was likely to succeed and we were in for four or eight more years of Obama. All that’s out the window now. You have at least the opportunity for the Republicans to demonstrate that they not only have a desire but an ability to govern smartly and get this country back on track.”

Leavitt said there were critical tasks for Trump beyond selecting senior White House aides and agency heads. He will be expected to craft a plan to turn his campaign priorities into legislative and executive actions; make initial contact with foreign leaders in an orderly and diplomatic way; and prepare to move his family to Washington.

“You’re going from campaigning to governance, and there’s a significant difference,” Leavitt said. “All of those are things that have to happen in 77 days [before the inauguration]. It’s a massive process.”

Patrick Caddell, a veteran pollster who is close to the Trump campaign, suggested that Trump “get away to Mar-a-Lago for a few days to rest and think” at his resort in Palm Beach, Fla., before fully diving into transition activities.

“He’s got to think through how to translate a popular uprising and movement into governing,” Caddell said. “He’s got to make sure the people he hires understand why he’s there and aren’t only from the management class or people who know him.”

Paul Kane contributed to this report.