Barack Obama has been frustrating the Democratic establishment of late. By refusing to endorse his former VP Joe Biden - who is barely clinging to his lead as the 2020 frontrunner, while at the same time panning progressive candidates such as Elizabeth Warren and Bernie Sanders, the former president appears to be tacitly admitting that the current pool of Democratic candidates - and Biden in particular, is not worth risking his reputation over.

Politico's Ryan Lizza sat down with several people in Obama's orbit, including former Attorney General Eric Holder - who wanted to run for President in 2020 but couldn't because of Biden.

Last year, Obama let it be widely known that he would not make his preference known or, in the phrase that his close advisers frequently use, “put his thumb on the scale.” It wasn’t just Biden who was disappointed. Holder was particularly wounded that his close friend wasn’t more encouraging of his own ambitions. ”He’s still pretty sensitive about it,” said someone close to Holder. “He was really frustrated about having arrived at the decision not to run. Holder couldn’t get in because Biden and Holder have the same set of people. Once Biden was getting in then Eric couldn’t get in. So that frustrated Holder. It blocked him. And Biden has turned out the way they all feared, and that’s really frustrating to Eric .” -Politico

The seemingly obvious answer as to why Obama won't endorse Biden is simple; they worked together for eight years, providing ample insight into Biden's gaffe-prone mental faculties and tone-deaf opinions - not to mention the whole Ukraine thing. Both Biden and Obama have stated that Biden asked Obama not to endorse him until he'd 'earned' it.

Instead, the former president has been dispensing advice to all 2020 candidates who seek it, and "sees his role as providing guardrails to keep the process from getting too ugly and to unite the party when the nominee is clear," according to the report.

That said, while Obama has been incredibly careful not to speak ill of Biden - he did take a jab at his former VP, suggesting that when it comes to having an 'intimate bond with the electorate' (especially in Iowa), Biden 'really doesn't have it.':

With several lesser-known candidates, according to people who have talked to him or been briefed on his meetings, he was blunt about the challenges of breaking out of a large field. His advice is not always heeded. He told Patrick earlier this year that it was likely “too late” for him to secure “money and talent” if he jumped in the race. Occasionally, he can be cutting. With one candidate, he pointed out that during his own 2008 campaign, he had an intimate bond with the electorate, especially in Iowa, that he no longer has. Then he added, “And you know who really doesn’t have it? Joe Biden.” -Politico

More takeaways from Politico:

Biden's camp has been frustrated with Obama's silence over Ukraine

One person who is very close to both Obama and Biden said the only time the Biden campaign has been disappointed in Obama is over Trump’s Ukraine scandal. “I don't think anybody in the Biden world challenges Obama’s affection for Biden, or challenges his strategy of not weighing in for anybody,” this person said. ”I do think there's frustration when Joe Biden and Hunter Biden get attacked by Republicans on the Ukrainian thing and they say, ’Obama and his administration looked the other way back when this was happening,’ and Obama doesn't say anything. The Biden people ask, ‘Why won’t Obama say something?’”

If Obama saw Bernie Sanders as a serious threat, he would actively campaign against him.

Obama said privately that if Bernie were running away with the nomination, Obama would speak up to stop him. (Asked about that, a spokesperson for Obama pointed out that Obama recently said he would support and campaign for whoever the Democratic nominee is.)

Obama offers candidates three big points: "Don’t run if you don’t think you are the best person to be president; make sure you understand the toll a campaign will take on your family; and ask yourself, “Can you win?”"

As he put it recently at a donor event in Washington, “Not are you guaranteed a win, but do you have a theory, a pathway whereby you win not just a primary but you also win a general election, because there is not an empty exercise if you, in fact, get in. Your goal should be to actually ultimately become the president and then be able to lead the country and the world in a serious way.”

Obama planned to focus on setting up his foundation, writing a memoir and dealing with global issues, but feels dragged back in by Trump's 2016 win.