Democratic presidential candidate, Sen. Cory Booker, D-N.J., speaks about gun control at Mother Emanuel AME Church, Aug.  7, 2019, in Charleston, S.C. Nine black Bible study participants were killed at the church in a 2015 racist attack.
FILE - Former Democratic presidential candidate Sen. Cory Booker.

WASHINGTON - New Jersey Sen. Cory Booker voiced support Monday for former U.S. Vice President Joe Biden's bid for the Democratic presidential nomination, his latest former challenger to endorse him just ahead of six state primary elections he faces Tuesday against Vermont Sen. Bernie Sanders.

Booker, who dropped out of the party's presidential contest in January before voting began a couple weeks later, said in a Twitter comment, “The answer to hatred & division is to reignite our spirit of common purpose. @JoeBiden won’t only win - he’ll show there’s more that unites us than divides us. He’ll restore honor to the Oval Office and tackle our most pressing challenges. That’s why I’m proud to endorse Joe.”

Booker's endorsement came a day after California Sen. Kamala Harris, who dropped out of the contest in December, endorsed Biden, saying that she felt that he was best prepared to "steer America through these turbulent times." 

Harris, often mentioned by U.S. political analysts as one of several possible vice-presidential running mates with Biden, said the U.S. needs a president "who reflects the decency and dignity of the American people, a president who speaks the truth; and a president who fights for those whose voices are too often overlooked or ignored."

FILE - U.S. Senator Kamala Harris launches her campaign for President of the United States at a rally at Frank H. Ogawa Plaza in her hometown of Oakland, California, Jan. 27, 2019.
Former Foe, Sen. Kamala Harris, Endorses Biden Presidential Bid
Vanquished Democratic opponents are supporting the former vice president's campaign against Trump

Several former rivals have now endorsed Biden, a list that also includes former South Bend, Indiana Mayor Pete Buttigieg and Minnesota Senator Amy Klobuchar. They both dropped out of the race for the Democratic presidential nomination just ahead of last week's Super Tuesday voting, when Biden won 10 of the 14 state party nominating elections over Sanders, a self-declared democratic socialist. Former New York Mayor Michael Bloomberg, who lost all 14 states to Biden and Sanders after spending more than $500 million of his own money on his campaign, also endorsed Biden last week.

A new CNN poll, taken after last week's party primary elections, shows U.S. Democratic voters favor Biden by a wide margin over Sanders, 52% to 36%. In Michigan, the auto-manufacturing hub in the U.S. where Biden and Sanders square off in a party primary election on Tuesday, several state-wide polls show Biden with a commanding lead.

The Democratic contest is to face Republican President Donald Trump in the November national election as he seeks a second term in the White House.

Biden on Sunday praised Harris as a political figure who has "spent your whole career fighting for folks who've been written off and left behind."

Civil rights leader Jesse Jackson endorsed Sanders, saying that "with the exception of Native Americans, African Americans are the people who are most behind socially and economically in the United States and our needs are not moderate. A people far behind cannot catch up choosing the most moderate path."

"The most progressive social and economic path gives us the best chance to catch up and Sen. Bernie Sanders represents the most progressive path," Jackson said.

Michigan has the most Democratic national convention delegates at stake in the Tuesday voting. The fivethirtyeight.com political forecasting site is predicting that Biden will win 81 of the state's 125 pledged delegates to 44 for Sanders.

The fivethirtyeight site gives Sanders a slight edge in the western state of Washington, where 89 delegates are at stake, with Biden ahead in the Midwestern state of Missouri and the Southern state of Mississippi. Forecasters say the two candidates are virtually even in two smaller states, Idaho and North Dakota.

Just a week ago, before the Super Tuesday voting, FiveThirtyEight.com  predicted that no Democratic candidate would be able to win the party nomination with a majority of delegates on the first convention ballot to face Trump.

Now, however, it predicts that Biden will cruise to victory on the first ballot, although neither Biden nor Sanders is close yet to a majority of delegates.

Sanders predicted on the "Fox News Sunday" show that he would win the Michigan vote.

"Joe Biden is a friend of mine," Sanders said. "Joe Biden is a decent guy."

But Sanders said the contest with Biden comes down to "which candidate is stronger in defeating Trump." He said he expects to win the key Michigan vote Tuesday and "certainly would not consider dropping out" if he loses.

"We won California, the biggest state in the country," Sanders said of last Tuesday's vote.

Sanders attacked Biden's vote as a senator for the American war in Iraq and trade deals with Canada and Mexico and another with Pacific Rim countries that Trump abandoned when he became president.

Biden and Sanders are scheduled to debate each other next Sunday.