U.S. Senator from Minnesota, Amy Klobuchar, and the former Mayor of South Bend, Indiana, Pete Buttigieg, are expected to endorse their once rival Democratic presidential contender Joe Biden.

Their decisions to back Biden come after both candidates dropped out of the 2020 U.S. presidential race, ahead of the critical Super Tuesday primary contests across 14 states.

Vermont Senator Bernie Sanders currently leads the delegate count to win the Democratic nomination to face off against President Donald Trump in November. But former Vice President Joe Biden is close behind, followed further back by Massachusetts Senator Elizabeth Warren. And former New York Mayor Mike Bloomberg will be on ballots for the first time on Tuesday.

Biden's campaign got a major boost after he decisively won South Carolina's primary on Saturday, helped by a high-profile endorsement from the highest-ranking African American to serve in Congress, South Carolina's Jim Clyburn.

Buttigieg and Klobuchar's backing of Biden is seen as an avenue to strengthen a more moderate path to the White House and block the more progressive Sanders from achieving an insurmountable delegate count lead.