WASHINGTON – Pete Buttigieg is endorsing former Vice President Joe Biden, just a day after the mayor suspended his campaign, according to the Associated Press.

Two people familiar with Buttigieg's decision say the former South Bend, Indiana, mayor will appear with Biden at a rally in Dallas on Monday night. They were not authorized to speak publicly and spoke to The Associated Press on condition of anonymity.

The move comes after Sen. Amy Klobuchar, who announced she is ending her campaign Monday, also threw her support to Biden. Both Klobuchar and Buttigieg were vying be the Democratic nominee through the same moderate lane. But the two former candidates' decision to endorse Biden shows moderates may be trying to rally behind one candidate as a singular alternative to Sen. Bernie Sanders, who is the current frontrunner.

Biden has seen a resurgence in his campaign following his blowout win in South Carolina on Saturday night. The former vice president was struggling to keep his campaign afloat following his fourth and fifth place finishes in Iowa and New Hampshire respectively.

More:Candidates flock to delegate-rich Texas with Super Tuesday around the corner

The endorsement will likely be a big boost for Biden heading into Super Tuesday. Biden's campaign efforts in many of the Super Tuesday states have trailed his top Democratic opponents, Sanders and former New York City mayor Michael Bloomberg.

Sanders is currently leading in polling in several key states for Tuesday's primaries, including California, Texas and is tied with Bloomberg in Virginia. Biden will need voters to coalesce behind him if he wants to be a competitive opponent to both Sanders and Bloomberg going forward.

Buttigieg on Sunday evening told supporters in South Bend that he was exiting the race to "help bring our party and our country together." Biden and Buttigieg talked on the phone Sunday evening, according to the Biden campaign.

Since then, Biden has seen a number of people who first endorsed Buttigieg switch their support to the former vice president, including Congressman Don Beyer of Virginia. Biden also got the endorsement of former Senate Majority Leader Harry Reid Monday. Reid had previously been quiet about who he might be supporting.

"Biden will be a much-needed stabilizing force following Trump’s disastrous term, offering a positive and progressive alternative to Trump’s dark vision of racism, xenophobia and policies built on cruelty and exclusion," he said in a statement. "I believe Biden is best able to defeat Donald Trump and enact the policies we all care about."

Reid, the former Senator from Nevada, did not endorse a candidate ahead of the Nevada caucuses on Feb. 22. Sanders went on to win there by a large margin.