(CNN) Former Vice President Joe Biden still isn't done with Hillary Clinton and the 2016 election -- and that may be why he refuses to rule out running again for president in 2020.

In an interview at a hedge fund conference in Las Vegas on Thursday, Biden said this of Clinton: "I never thought she was a great candidate. I thought I was a great candidate."

If you're surprised by Biden running down Clinton, you haven't been paying close attention to the former vice president's utterances. Lucky for you, I have!

"What happened was that this was the first campaign that I can recall where my party did not talk about what it always stood for -- and that was how to maintain a burgeoning middle class. You didn't hear a single solitary sentence in the last campaign about that guy working on the assembly line making $60,000 bucks a year and a wife making $32,000 as a hostess in restaurant."

"I don't think she ever really figured it out," Biden told Memoli of the underlying message of Clinton's campaign. "And by the way, I think it was really hard for her to decide to run." Biden added: "She thought she had no choice but to run. That, as the first woman who had an opportunity to win the presidency, I think it was a real burden on her."

"I believe we have to end the divisive, partisan politics that is ripping this country apart and I believe we can. It's mean spirited. It's petty. And it's gone on for much too long. I don't believe, like some do, that it's naive to talk to Republicans. I don't think we should look at Republicans as our enemies. They are our opposition. They're not our enemies."

Yes, of course, Biden endorsed Clinton shortly after the never-ending Democratic primary fight between the former Secretary of State and Vermont Sen. Bernie Sanders ended. And yes, even in this latest interview in Las Vegas, Biden made clear that "Hillary would have been a really good president."

But that was -- and is -- simply political box-checking. Biden's real -- and far more negative -- feelings about Clinton are exposed in the long arc of his comments about why she lost and why she was never a terribly good candidate.

The origin of all of this? Hard to pin down exactly. After all, Biden and the Clintons have been circling each other for decades in the Democratic political orbit. Any time two ambitious people are around each other for that long, there are always slights -- real or imagined -- and grudges.

Biden's antipathy toward Clinton's 2016 bid in particular, however, is a bit more easy to trace. He quite clearly viewed himself as the logical heir to the legacy of outgoing President Barack Obama. But Clinton, from the start of the campaign, seized that mantle and ran with it.

By the time Biden emerged from the initial shock and grief of the death of his oldest son, Beau, in May 2015, it was already too late -- a fact he acknowledged in bowing out of the race formally in October of that year. Clinton had consolidated enough of the Obama coalition that it would have been next to impossible for Biden to claw it back from her.

Circumstances made it impossible for Biden to run in 2016. But that never meant that he thought Clinton was any great shakes as a candidate. Or that she was right to have run as Obama's heir. Or that Biden didn't regret that he never got the chance to make the case himself for why the principles of the Obama-Biden White House were the right ones for the country for the next four years.

"I regret it every day," Biden said in January 2016 of his decision not to run . "But it was the right decision for my family and for me. And I plan on staying deeply involved."

"Deeply involved" could well mean a third run for president for Biden in 2020.

"Could I? Yes," Biden said Thursday. "Would I? Probably not."

If Biden, who would be 78 in 2020, did decide to run, it would be about himself, sure. But it would also be about proving to himself and the world that he could run the campaign Hillary Clinton never could.