This story has been updated.

Just a few days in advance of next Tuesday's Vermont primary, U.S. Rep. Peter Welch (D-Vt.) saw one of his two Democratic challengers drop out of the race and endorse the other.

He literally saw it, because it happened during a live debate on Vermont Public Radio Thursday with all three candidates in the same studio.

Ben Mitchell, an educator from Westminster, took part in the debate and then, during his closing statement, announced he was withdrawing and endorsing Dan Freilich, a physician from Brownsville. Both candidates have made campaign finance a centerpiece of their efforts to defeat Welch, who routinely raises most of his money from corporations and political action committees. As of July 15, Welch's campaign fund had a balance of nearly $2.1 million.

"Because, Peter, you have taken money from corporations ... your decisions will be colored by that," Mitchell said, addressing Welch directly. He then turned to Freilich and said, "We don't agree on everything, but I think we need someone to represent Vermont who does not represent the corporations."

Freilich replied that he was "humbled and honored" by Mitchell's endorsement.

When reached by phone after the debate, Freilich acknowledged that he knew in advance what Mitchell intended to do. "We had a discussion a couple of days ago," Freilich said. "He told me he was going to announce it [during the debate]. He asked me to keep it quiet."

Freilich thanked Mitchell for "fighting the good fight," and for realizing that "the best way to fight the good fight was to drop out and ask his supporters to vote for me."

"Dan is a sincere individual who's trying to do what's right for Vermont," Mitchell said in an interview late Thursday afternoon. "He's worked hard, he's raised more money than I have, and I think he has a better chance to win."

Mitchell's name will remain on the ballot, but his withdrawal essentially leaves Freilich as the sole option for Democratic primary voters concerned with Welch's acceptance of corporate cash. But Freilich is still a long shot in Tuesday's primary, since Welch is broadly popular with Democratic voters.