Despite Joe Biden’s commanding victory in Saturday’s South Carolina primary, in which he garnered close to 50 per cent of the vote, an endorsement from the president with whom he served seems not to be forthcoming.

Speaking to CNN, a source close to Barack Obama said that in a congratulatory phonecall after Mr Biden’s victory, the president told Mr Biden he would not be endorsing him any time soon, citing worries that he could badly divide the party during a still-messy nominating process.

Explaining the president’s thinking, the source said that for now, the risks outweigh the rewards: “We are sceptical that an endorsement coming from us could truly change the political winds right now.

“Weighing in now likely only divides things worse and weakens his standing for when the party will need it most.”

Mr Biden routinely invokes the legacy of the Obama administration as part of his campaign pitch, including in TV ads that make clear how highly the former president thinks of him. However, he has also made clear he does not feel entitled to a blessing, saying “I have to earn this on my own”.

Barack Obama's best moments in the White House Show all 11 1 /11 Barack Obama's best moments in the White House Barack Obama's best moments in the White House May 19, 2009 “The President was leaving the State Floor after an event and found Sasha in the elevator ready to head upstairs to the private residence. He decided to ride upstairs with her before returning to the Oval Office,” Peter Souza Barack Obama's best moments in the White House Oct. 26, 2012 President Barack Obama pretends to be caught in Spider-Man's web as he greets the son of a White House staffer in the Outer Oval Office Peter Souza Barack Obama's best moments in the White House “A National Security staffer, Carlton Philadelphia, brought his family to the Oval Office for a farewell photo with President Obama. Carlton’s son, Jacob, softly told the President he had just gotten a haircut like President Obama, and asked if he could feel the President’s head to see if it felt the same as his.” Peter Souza Barack Obama's best moments in the White House March 21, 2010 The President, Vice President and senior staff applaud after watching on television the House vote on H.R. 4872 for health care reform, in the Roosevelt Room of the White House Peter Souza Barack Obama's best moments in the White House Dec. 3, 2009 President Barack Obama fist-bumps custodian Lawrence Lipscomb in the Eisenhower Executive Office Building following the opening session of the White House Forum on Jobs and Economic Growth Peter Souza Barack Obama's best moments in the White House Sept. 22, 2015 "The Obama family and Biden family greet Pope Francis as he arrives in the United States for the first time at Joint Base Andrews," Sept. 22, 2015. Peter Souza Barack Obama's best moments in the White House Feb. 21, 2014 President Barack Obama and Vice President Joe Biden participate in a "Let's Move!" video taping on the Colonnade of the White House, Feb. 21, 2014 Peter Souza Barack Obama's best moments in the White House Feb. 18, 2016 President Barack Obama watches First Lady Michelle Obama dance with 106-Year-Old Virginia McLaurin in the Blue Room of the White House prior to a reception celebrating African American History Month, Feb. 18, 2016 Peter Souza Barack Obama's best moments in the White House Jan. 21, 2013 "The President and First Lady wave to supporters as they ride in the inaugural parade. I had asked the President if I could ride in the presidential limousine and the President joked, 'But Michelle and I were planning to make out," Jan. 21, 2013. Peter Souza Barack Obama's best moments in the White House Barack Obama and former First Lady Michelle Obama share a private moment in a freight elevator at an Inaugural Ball, January 2009 all pics: Pete Souza Barack Obama's best moments in the White House Barack Obama rests his hand on the bible that President Lincoln used for his swear-in, being held by his wife Michelle Obama as he is sworn in as the 44th President of the United States of America Rex

However, Mr Biden did speak up to demand TV stations pull a misleading ad that used his words out of context to imply he himself was attacking Mr Biden.

Mr Biden has also accused his rival Bernie Sanders of undermining the former president, including plotting to run against him as he stood for re-election in 2012. Mr Sanders denies he ever planned to do such a thing.

Since his South Carolina triumph, Mr Biden has quickly returned to his onetime position as Mr Sanders’s principal challenger, and he is polling well in many of the states due to vote on Super Tuesday.

That has added to the pressure on other candidates to drop out and allow Mr Biden to consolidate the “anti-Sanders” vote.

Pete Buttigieg, who tied with Sanders in Iowa and ran a close second in Iowa but afterwards performed poorly, dropped out after South Carolina. That leaves Mr Biden, Elizabeth Warren, Amy Klobuchar and Michael Bloomberg as Sanders’s “moderate” rivals.