United States President Joe Biden's prospects of running for a second presidential term are dimming, according to bettors on the crypto-based prediction market Polymarket, as speculation over the incumbent commander in chief's mounting health issues cast doubt on his fitness for the country's top office. 

A Polymarket betting pool holding more than $135 million in cryptocurrencies shows 60% of traders are betting that U.S. Vice President Kamala Harris will clinch the Democratic presidential nomination by August 21. By comparison, just 28% of users are placing their bets on Biden topping the ticket.

Meanwhile, roughly 10% of bettors are putting odds on other potential candidates, including Michigan Gov. Gretchen Whitmer, Polymarket data shows. The chances of Harris securing the nomination rose as high as 64% earlier Thursday.

Bettors’ crashing confidence in Biden's ability to secure the Democratic presidential nomination marks a sharp contrast to their previous predictions. Last week, bettors had Biden's odds of running for re-election at roughly 74%, according to a screenshot of Polymarket data shared on Twitter (aka X) by pseudonymous Coinbase engineer Yuga.eth. 

The stunning reversal of those odds comes amid a report from The Washington Post that President Barack Obama has expressed doubts about the “viability” of Biden's second presidential run to his political allies, and just a day after Biden revealed he had been diagnosed with COVID-19.

The diagnosis came on the heels of widespread public speculation about the octogenarian president’s mental fitness to run for office, following Biden’s poor performance during a public debate with Republican challenger Donald Trump last month.

Prediction markets have occasionally proven to be more accurate barometers of voter behaviors than traditional polling methods. PredictIt, a prominent prediction market, touted in a public statement that its traders accurately called electoral college outcomes in seven battleground states during the U.S. presidential election in 2020.

Meanwhile, many political commentators criticized pre-election polling data that year for overstating Biden's lead over Trump, according to a report from nonpartisan think tank Pew Research Center. Still, experts remain divided on whether prediction markets can consistently predict the outcomes of future events.

Edited by Andrew Hayward