A Polymarket trader has seen their profits skyrocket following President Joe Biden's announcement on Sunday that he will not seek re-election in November.

The trader, operating under the username "RevengeTour19B4," holds positions in several political prediction markets, including punts on the outcome of Vice President Kamala Harris’ White House Bid.

The user purchased 671,081 shares, predicting Harris's nomination at an average price of around $0.28 per share, according to data from Polymarket. The last time the bet traded at that level was July 18, just days before Biden announced his intentions to drop out of the race.

Following Biden's endorsement, the market price for these shares surged to $0.90, resulting in a position size of around $601,000 and an unrealized gain of roughly $410,000 — a 217% increase.

Biden's decision to withdraw from the 2024 race came after repeated pressure from Democratic colleagues, who were concerned about his health and age.

While unsurprising to some, Biden’s subsequent endorsement of Harris for the Democratic presidential nomination is viewed as an attempt to sway voters back to the party.

"Today, I want to offer my full support and endorsement for Kamala to be the nominee of our party this year," Biden wrote on Sunday. "Democrats — it’s time to come together and beat Trump. Let’s do this."

His endorsement, delivered via a social media post to X, sent shockwaves throughout the political landscape, bolstering Harris’ chances in the primary field.

That has propelled RevengeTour19B4's rankings to the top of the Polymarket profit leaderboard — to the tune of $837,800, alongside a top spot for total volume at $34.69 million.

The endorsement also led to immediate reactions in the prediction markets, with Polymarket clocking its record-setting $24 million in bets in a single day on Monday.

Traders, anticipating a significant boost to Harris's campaign, quickly adjusted their positions, driving up the prices of shares predicting her success. Harris is now predicted to win the Democratic nomination with a 90% chance, data shows.

The mechanics that underpin Polymarket trading are relatively straightforward. The price of one “share” in a prediction market ranges from between $0.00 to $1, and its price correlates to its percentage chance of winning, or its “odds.”

RevengeTour19B4's bets on Harris would, theoretically, pay handsomely, provided the trader successfully liquidates their shares once the bet concludes.

For the market predicting Harris' victory in the 2024 U.S. Presidential Election, the trader also acquired 512,914 shares at an average price of $0.12 each. 

The share price has since increased to $0.33, bringing the current value of this position to around $167,000, reflecting an unrealized gain of roughly $106,000, or a 174% rise.

The trader's portfolio also includes positions on other political outcomes, such as the general election and the possibility of prominent Democrats, like Michelle Obama, entering the race, though the largest gains have been tied to Harris' fortunes.