Pete Buttigieg, the openly gay U.S. presidential candidate, on Sunday ended his campaign to be the Democratic nominee, giving a major boost to fellow centrist Joe Biden.

The 38-year-old Buttigieg's surprise decision was set to shake up the race this week when 14 states vote on "Super Tuesday."

It is expected to further boost the fortunes of Biden after the former vice president scored a resounding victory in South Carolina's primary on Saturday in the contest to see who faces President Donald Trump in November.

Biden has emerged as the chief moderate challenger to frontrunner Bernie Sanders, the firebrand leftist who has taken the race by storm and is looking to score big wins on Tuesday in states such as crown jewel California.

Buttigieg, a military veteran and former mayor of South Bend, Indiana, addressed supporters in his home town. Buttigieg did not mention Sanders by name in his speech, but he has publicly stated he believes the 78-year-old senator's "inflexible" political approach would fail in a match-up against Trump.

Sanders continues to hold poll leads in several Super Tuesday states, including California. "I think we've got a great chance to win in California, in Texas, in Massachusetts and a number of states," Sanders said Sunday on CBS.

On Monday, Biden campaigns in Texas, Super Tuesday's second largest haul of the delegates, who formally pick the party's nominee in July, while Sanders campaigns in Utah and in Klobuchar's home state of Minnesota.