The 77-year-old Biden also responded forcefully to a suggestion by the questioner that he was "too old" to be running for president.
Harris was among first major Democratic Party leaders to announce her presidential run in last January, which was attended by a massive crowd of over 20,000 supporters
In a wide ranging discussion, Sandberg touched on other big themes for 2020, including antitrust investigations and political ads.
Arizona has received scant attention form the Democrats running for president, but Bloomberg has put a heavy focus in a state he said will be crucial to the general election.
Bloomberg, who ran New York from 2002 to 2013, registered on Thursday with the US Federal Election Commission -- another step towards a run at the White House.
The freeze was welcomed by the vaping industry, which has been blamed for a health epidemic among teenage consumers of their products
In a 30-day period between August and September, the group, called "Phosphorous" by the company, made more than 2,700 attempts to identify consumer email accounts belonging to specific customers
Unlike his predecessors, Trump has not released his annual tax returns
US Trade Representative Robert Lighthizer and Treasury Secretary Steven Mnuchin are headed to Shanghai next week for resumption of trade talks with China
A simple statistical model applied to recorded approval ratings shows Trump has been garnering higher and higher approval ratings since taking office
Much of Trump's spending on Facebook advertising in recent weeks has gone toward ads that have been seen by older Americans
An unprecedented rise in the number of presidential candidates running for 2020 has raised many queries
Singh, an engineer from Atlantic County who works in the aerospace and defence industries, filed his campaign committee with the Federal Election Commission on Wednesday
Biden closely followed by Sanders, who unsuccessfully ran for the nomination against Hillary Clinton in 2016
Clinton has held meetings with some of the Democrats who are now vying for the party nomination or considering a run
Warren's past battles with Wall Street have brought her a large following, and her campaign team has drawn the grudging respect of its rivals
The President also lags behind television personality Oprah Winfrey between 41 to 52 percent