Facing sustained criticism from rival Democratic presidential hopefuls over his ritzy wine cave fundraiser and billionaire contributors, South Bend, Indiana Mayor Pete Buttigieg's 2020 campaign this week launched a "contest" to see which supporter can give the candidate the smallest unique donation—a competition that's conveniently timed just ahead of the fourth-quarter filing deadline.

"The Pete for America Innovation Team out there working hard on Christmas Eve coming up with gimmicks to lower his average donation amount this quarter. Funny stuff."

—Tim Tagaris, senior adviser to Sen. Bernie Sanders

Buttigieg's campaign described the contest as an innocuous "end of year guessing game," but critics condemned it as a gimmick that appears designed to lower the mayor's average donation for the final quarter of the year and create the impression of a genuine surge in grassroots enthusiasm.

Through three quarters of fundraising, Buttigieg's average donation has been around $40, significantly higher than the $18 and $27 averages boasted by Sens. Bernie Sanders (I-Vt) and Elizabeth Warren (D-Mass.), respectively.

"Instead of just ending private fundraisers with wealthy donors and refusing to accept donations from billionaires, Pete's campaign rolled out this cynical ploy to skew the average donation amount by flooding the pool with mass donations of a few pennies," tweeted progressive activist Jordan Uhl. "What a fucking joke."

In a Christmas Eve email to supporters, the "Pete for America Innovation Team" explained the contest:

All you have to do to win is donate the smallest amount that nobody else donates. In other words, suppose you donate $1.00. If someone else playing also donated exactly $1, you both lose. We'll see if only one player donated $1.01, and so on until we find an amount donated exactly once, and that's our winner. That's it—those are the rules! Only donations that are part of this contest count (from this email, and let's be real, we might send you a reminder or two but that's it). Multiple donations are allowed; just be creative, pick a unique donation amount, and you could win.

Tim Tagaris, a senior adviser to the Sanders campaign, highlighted the email on Twitter, calling the competition "transparently hilarious."

"The Pete for America Innovation Team out there working hard on Christmas Eve coming up with gimmicks to lower his average donation amount this quarter," wrote Tagaris. "Funny stuff."

The Pete for America Innovation Team out there working hard on Christmas Eve coming up with gimmicks to lower his average donation amount this quarter. Funny stuff. pic.twitter.com/D1fbQp0t9Q — Tim Tagaris (@ttagaris) December 25, 2019

"The only reason to do this is to rig the stats," tweeted activist Rafael Shimunov. "Buttigieg wants to diversify the amounts here, so that in financial filings it doesn't look suspiciously like the same amount. Encouraging supporters to think up random tiny amounts to make it appear natural and not rigged."

"The only reason to do this is to rig the stats."

—Rafael Shimunov

The contest comes just days after Warren and Sanders both took aim at Buttigieg over his now-infamous wine cave fundraiser in Napa Valley, California and his dozens of billionaire campaign contributors.

"Billionaires in wine caves should not pick the next president of the United States," Warren said during the Democratic presidential debate in Los Angeles last week.

Sanders piled on, scathingly mocking the "real competition" between Buttigieg and former Vice President Joe Biden over who has the most billionaire donors.

"My good friend, Joe, and he is a good friend, he's received contributions from 44 billionaires. Pete, on the other hand, he's trailing... You only got 39 billionaires contributing," Sanders said. "So, Pete, we look forward to you—I know you're an energetic guy and a competitive guy—to see if you can take on Joe on that issue."

Ahead of the debate, Buttigieg drew outrage by leaving more than twenty major bundlers off a list of top fundraisers his campaign released last week—omissions the campaign said were inadvertent.

"The first time I saw this list, I said, 'There is no way this is comprehensive," Jeff Hauser, executive director of the Revolving Door Project, told Politico. "It's just kind of mind-blowing that they would be this dishonest."