Former President Barack Obama has reportedly expressed doubts to former Vice President Joe Biden about his bid for the 2020 presidential nomination.

Obama gently urged Biden against running, but the former vice president said he felt he had an obligation to take on President Donald Trump, according to a New York Times report.

Obama reportedly told Biden's advisers to not let the former vice president "damage his legacy" along the campaign trail.

Obama, who remains popular in his post-presidency, has not endorsed anyone in the 2020 Democratic primary. But his legacy has at times emerged as a point of debate among 2020 Democrats.

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Former President Barack Obama and Joe Biden have an extremely close relationship, but that reportedly hasn't alleviated concerns Obama has about the former vice president's 2020 campaign.

Obama spoke with Biden about the prospect of him running multiple times before the former vice president hopped into the race, and "took pains to cast his doubts about the campaign in personal terms," according to a New York Times report.

A person familiar with the exchange told The Times that Obama said to Biden, "You don't have to do this, Joe, you really don't." But Biden responded that he felt he had an obligation to take on President Donald Trump and that he wouldn't be able to forgive himself if he didn't give it a shot.

Obama has not endorsed anyone in the wide field of 2020 Democrats, but has apparently taken a special interest in his former vice president's campaign.

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He is concerned that Biden is relying on advisers who are "too old and out of touch with the current political climate," according to The Times, and has urged the former vice president to hire younger aides.

The report also said Obama asked some of Biden's top advisers to ensure the former vice president doesn't "damage his legacy" or "embarrass himself" during the campaign.

A spokesperson for Obama did not immediately respond to a request for comment from INSIDER.

Obama remains highly popular with voters, but his legacy has emerged as a point of contention among 2020 Democrats at times. Biden has been accused by his 2020 opponents of leaning too heavily on his relationship with Obama to gain points along the campaign trail.

"You invoke President Obama more than anybody in this campaign. You can't do it when it's convenient and then dodge it when it's not," Sen. Cory Booker of New Jersey said to Biden during a heated exchange amid the presidential debate in Detroit last month.

Despite a series of gaffes in recent weeks, a wide set of polling shows that Biden remains the frontrunner for the 2020 Democratic nomination.