WASHINGTON • For months, US President Barack Obama said that Mr Donald Trump was unqualified, temperamentally unfit and a threat to the republic who should never be president.

For years, Mr Trump questioned Mr Obama's birthplace and legitimacy, branded the nation's first black president weak and called his tenure a disaster.

On Thursday at the White House, the once-unimaginable happened: The two men met face to face for the first time for a 90-minute discussion in the Oval Office and shook hands, making a public show of putting their bitter differences aside.

The meeting effectively launched the transition that will unfold over the next 10 weeks until Mr Trump is sworn into office on Jan 20.

"I want to emphasise to you, Mr President-elect, that we now are going to want to do everything we can to help you succeed because if you succeed, then the country succeeds," Mr Obama told Mr Trump after the meeting as the two sat side by side two days after Mr Trump's stunning election upset imperilled Mr Obama's legacy.

The President called the conversation "excellent" and said he had been "encouraged" by Mr Trump's interest in working with him and his team.

Mr Trump, who appeared nervous and uncharacteristically subdued beside Mr Obama, called the President "a good man". He said that the meeting was "a great honour" and that their conversation had lasted far longer than he would have expected.

"I have great respect," Mr Trump said, turning to face Mr Obama. "We discussed a lot of different situations, some wonderful, and some difficulties. I very much look forward to dealing with the President in the future, including counsel."

Given that Mr Trump has never held elective office or served in government, some administration aides suggest that Mr Obama could play a larger-than-usual role in acquainting Mr Trump with the demands of the office.

"The meeting might've been at least a little less awkward than some might have expected," said Mr Josh Earnest, the White House press secretary.

Aides said that the two men discussed foreign and domestic policy issues that Mr Trump would need to deal with on Day One in the Oval Office.

As early as yesterday, the President-elect was to get a version of the President's Daily Brief, a classified compilation of all threats facing the United States and other highly significant intelligence information.

Outside in the Rose Garden, reporters could see Mr Denis R. McDonough, the White House chief of staff, emerge from the West Wing talking in hushed tones with Mr Jared Kushner, the President-elect's son-in-law and adviser. Speculation has emerged that Mr Kushner, who is married to Mr Trump's daughter Ivanka, could be the next chief of staff.

Top advisers to Mr Obama have spent months preparing for the transition, a complex venture condensed into the 72 days before the inauguration.

It is up to them and the Trump team to set it in motion, pairing Obama administration staff members with representatives of the President-elect for crash courses in the workings of the White House and federal agencies.

Mr Obama said on Wednesday that he had instructed his staff to follow the example set by President George W. Bush in 2008 and provide a professional and smooth transition for Mr Trump's team, despite the policy differences that separate the President and his successor.

For all the public drama and division of the presidential campaign, Mr Obama's aides have been quietly working with advisers to Mrs Hillary Clinton and Mr Trump since July to plan for the passing of power.

Next month, Mr Obama's team plans to hold the first of two war-gaming exercises to prepare Mr Trump and his staff for a potential national security crisis. The second simulation for Mr Trump is set for January, days before he officially gains access to the nuclear codes.

Yesterday, retired neurosurgeon Ben Carson, who became a Trump adviser after dropping out of the Republican presidential nomination, confirmed that he is "having discussions" with the Trump team about being in the new Cabinet.

Mr Trump's campaign manager, Ms Kellyanne Conway, also announced on Twitter that she has been offered a job in the White House, although she did not elaborate.

NYTIMES