Pete Buttigieg apparently caught his rivals for the 2020 presidential election off guard Sunday evening after abruptly pulling out the race.

The announcement from the former mayor of South Bend, Ind., came less than a month after he declared victory in the contested Iowa caucuses and ahead of Super Tuesday, in which 14 states are set to head to the polls and one-third of all delegates for the nomination will be at stake.

The Democrat's rivals weighed in on his departure.

Sen. Bernie Sanders, I-Vt., told reporters in Los Angeles that Buttigieg ran "a brilliant campaign," adding, "I just want to welcome all of his supporters into our movement and urge them to join us in the fight for real change in this country."

"Thank you, @PeteButtigieg. I know you'll continue giving back and serving our country for many years to come," Sen. Elizabeth Warren, D-Mass., tweeted.

Sen. Amy Klobuchar, D-Minn., who was trailing behind Buttigieg in the latest RealClearPolitics poll average, wrote on Twitter that Buttigieg had run "an inspiring and historic campaign," referring to him being the first openly gay candidate to run for president.

"I have so much respect for you @PeteButtigieg and know there are great things ahead. And both John and I are big fans of Chasten!" she tweeted, referencing their husbands.

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Former Vice President Joe Biden, who scored a wide victory in Saturday night's South Carolina primary, likewise praised Buttigieg for running a "historic" campaign based on "courage, compassion, and honesty."

Buttigieg, an Afghanistan war veteran, had been critical of Biden, charging that the 77-year-old lifelong politician was out of step with modern politics. But, his criticism more recently shifted toward Sen. Bernie Sanders, I-Vt., who was benefiting from the number of candidates dividing up the moderate vote.

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Throughout his campaign and on the debate stage, Buttigieg portrayed himself as a compromise candidate between the party's progressive and establishment wings. He drew admirers for his calm, reasoned demeanor and rhetorical skills that reflected his Harvard-trained, Rhodes scholar background -- but some voters and operatives described it as "robotic."

Fox News' Andrew Craft, Gregg Re and The Associated Press contributed to this report.