(CNN) Almost 6 in 10 Americans have a favorable opinion about Joe Biden in a new CNN national poll , a finding sure to give the Democratic former vice president a boost as he considers whether to run for president in 2020.

The 57% favorable rating is Biden's best in CNN polling since February 2009 -- when he was sworn in as Barack Obama's vice president. Just over 1 in 4 (27%) have an unfavorable view of Biden.

What's remarkable about those numbers is how Biden's favorability has surged since he (and Obama) left office. As recently as March 2015, CNN polling showed more people viewed Biden unfavorably (46%) than regarded him favorably (43%).

The recovery of Biden's numbers stands in stark contrast to the ongoing negative view that Americans hold of Hillary Clinton, the Democratic Party's 2016 presidential nominee; in Gallup polling released earlier this week, Clinton's favorable rating dipped to 36%

What explains Biden's current popularity? A few things:

He drew hugely laudatory coverage earlier this year for his book tour in support of his memoir about the loss of his eldest son, Beau.

Politicians -- with the notable exception of Clinton (of late) -- always grow more popular when out of office.

Some level of buyer's remorse -- particularly among Democrats -- who believe that had Biden run in 2016, he would have easily beaten Donald Trump.

Biden has been open about his thinking on running for president in 2020, which would be his third bid for the nation's highest office. "If I were offered the nomination by the Lord Almighty right now, today, I would say no because we're not ready, the family's not ready to do this," Biden said on "The View" earlier this month. "If, in a year from now, if we're ready, and nobody has moved in that I think can do it, then I may very well do it."

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While Biden has made no decisions, he's doing the sorts of things someone running for president does in these early stages. He has apologized for his less-than-robust defense of Anita Hill during Clarence Thomas' Supreme Court confirmation hearing in 1991. He has traveled the country in support of Democratic candidates. And so on.

What's so interesting about the CNN poll is that it not only shows why Biden is clearly a top-tier candidate if he runs for president but it also reveals his potential Achilles' heel in that race.

When asked whether "the country would be governed better or governed worse if more women were in political office," almost two-thirds of Americans (64%) said the country would be better off with more women in office. Just 10% said things would be worse with more women in elected office, while 16% said it wouldn't make much difference.

Why is that relevant to Biden? Because he is a 75-year-old white man considering a run for president amid the #metoo movement and a cultural awakening about the boorish -- and in some cases criminal -- behavior by men toward women in the workplace.

That a large majority of people believe the country would be better off with more women running things suggests a major opening exists for a female politician to make a very credible run for the Democratic nomination in 2020.

At the moment, none of the female candidates who might run are even close to as well known as Biden. One example: More than half of the country -- 55% -- didn't know enough about New York Sen. Kirsten Gillibrand to offer an opinion about her in the new CNN poll

But, it's 2017. Which means Gillibrand, who has become a leading voice of the #metoo movement in Congress, has plenty of time to get better known and to challenge the likes of Biden for the nomination.

That is a worry for another day for Biden and his allies, however. Today they will revel in his popularity and use those positive numbers to build buzz for a 2020 bid.