Vice President Kamala Harris is now tied with former president Donald Trump at 49% among bettors looking to predict the next occupant of the White House on crypto prediction platform Polymarket. The wager is the single largest betting pool on the site, with over $541 million riding on the contest.

The milestone comes the day after Harris announced Minnesota Gov. Tim Walz as her running mate—a development that confounded Polymarket users that had heavily favored Pennsylvania Gov. Josh Shapiro.

As Polymarket noted the tie on Twitter, Harris and Walz—as well as Donald Trump's running mate, J.D. Vance (R-OH)—are both campaigning in Michigan.

Harris odds on the site have risen steadily since July 21, when Biden dropped out. At the time, her odds were 30% compared to Trump’s at 64%. At that point, as Biden was recovering from COVID-19 and rumors of his withdrawal were widespread, the president's odds had already slipped to 7%.

Prediction markets like Polymarket are often touted as meaningful sources of probabilities and predictors of market sentiment, in contrast to public opinion polls. Prediction market participants are self-selecting, however, and Polymarket, in particular, skews heavily in favor of crypto users, which uses Polygon, a layer-2 scaling solution on the Ethereum blockchain.

Polymarket odds are often quick to react to breaking news, such as the assassination attempt on Trump. Harris’ choice of Walz over Shapiro on Tuesday, meanwhile, shows that prediction markets can miss the mark.

The platform recently picked up prominent statistician Nate Silver as an advisor. Silver's previous polling aggregator, FiveThirtyEight, is now owned by ABC under the name 538, while Silver publishes his own analysis as Silver Bulletin.

Polymarket has been experiencing explosive traffic and popularity in recent weeks, driven largely by the presidential race and U.S. politics. In July, an incredibly chaotic month that included an attempted assassination of Trump and President Joe Biden withdrawing from the race—the site facilitated a record $387 million in trading volume, according to a Dune dashboard. That was more than triple its volume in June.

In fact, one week into August, Polymarket has already racked up $130 million in trades.