President Obama Hasn't Ruled Out Endorsing Joe Biden or Hillary Clinton in 2016

— -- The assumption is that President Obama will stay neutral if Joe Biden challenges Hillary Clinton in the Democratic presidential primary. But that’s not necessarily so, the White House said today.

“I wouldn’t rule out the possibility of an endorsement in the Democratic primary,” White House Press Secretary Josh Earnest responded to a question posed by ABC News' Jonathan Karl in a White House briefing.

But how exactly the president would handle a hypothetical Clinton-Biden contest remains an open question.

“There's not an insignificant ‘if’ in that question and that’s what everybody is pretty interested to find out,” Earnest said. “The president has indicated his view that the decision that he made seven years ago now to add Joe Biden to the ticket as his running mate was the smartest decision he ever made in politics.”

Speculation about a Biden 2016 run escalated this weekend after a hastily arranged secret meeting between the vice president and Sen. Elizabeth Warren, D-Mass., a liberal firebrand many had urged to step into the presidential race.

The briefing came at the same time as Obama and Biden sat down for a private lunch. The two men meet for lunch on a weekly basis when they are both in town. The White House has not offered a readout of the lunch.

Asked whether Biden, 72, is the legitimate heir of the Obama legacy, Earnest would not answer directly but did say that a large part of what has been accomplished during the Obama presidency “would not have been possible” without Biden.

While Earnest was not shy in praising Biden from the briefing room podium, he also volunteered some warm words for Clinton, 67.

“The president has spoke[n] at quite some length about the appreciation respect and admiration he has for the service of Secretary Clinton, particularly during her four years as secretary of state,” Earnest said, before once again pivoting to praise the vice president.

“I’ll just say that vice president is someone who has already run for president twice, he's been on a national ticket through two election cycles now,” he said. “So I think you could make the case that there is no one in American politics today who has a better understanding of what is required to mount a successful national presidential campaign.”