His comments came during a finance conference in Las Vegas.
But Biden didn't point to any specific moment.
While discussing Clinton's 2016 candidacy, Biden told the crowd, "I never thought she was the correct candidate. I thought I was a great candidate".More news: Former Fox News CEO Roger Ailes died after fall in home
Biden didn't target President Trump directly, but he did appear to allude to the recent turmoil in the White House.
As for whether or not we could see a presidential run from Biden for the 2020 election, Biden said, "Could I? Yes".
Biden will be 78 by the next election. He had previously lamented the lack of outreach to working class voters on the part of the Clinton campaign, saying "We didn't talk to them". The Obama administration viewed a potential Clinton administration as one that would carry on the the legacy of the Obama years.
Vice President Joe Biden shakes hands with Treasury Secretary Timothy Geithner as Secretary of State Hillary Rodham Clinton looks on at center, during the opening session of the joint meeting of the U.S. I thought I was a great candidate'. "Could I run? Yes".More news: Trump Wants Michael Flynn Back in White House
Republican presidential candidate Donald Trump (L) jokes with retired Gen. Michael Flynn as they speak at a rally at Grand Junction Regional Airport on October 18, 2016 in Grand Junction, Colo. I didn't run for one simple, overarching reason. "That's the total reason", Biden said. But Biden said Obama promised him he'd be the last guy in the room on every important issue - a promise that was ultimately kept.
Biden called Obama "absolutely, totally competent" and said he took his job "extremely seriously", but acknowledged that the former president had made some mistakes.
Biden will turn 77 in 2020.
The 74-year-old also addressed speculation that he could run for president in 2020.More news: Iran's re-engagement with the world at stake in Friday presidential vote
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