US Vice President Joe Biden announces he will not seek the 2016 Democratic presidential nomination with President Barack Obama and his wife Jill at his side during an appearance in Rose Garden of the White House in Washington October 21, 2015. [Photo/Agencies]

"I don't think we should look at Republicans as our enemies. They are our opposition, they're not our enemies," Biden said.

Speculation about a Biden candidacy had grown as Clinton slumped in polls and questions grew about her honesty and trustworthiness amid the controversy over her use of a private email server while secretary of state.

But what was widely hailed as a command performance by Clinton in the Oct. 13 Democratic debate turned the tide back in her favor and quieted talk that she was vulnerable in her quest for her party's nomination for the November 2016 election.

A Clinton spokesman said she called Biden after he announced his decision. In a statement, she called him "a good man and a great vice president" and said she was confident he would continue to be on the political front lines.