Some, such as the online political stock market PredictIt, have seen record volume during the last two days on contracts focused on whether Trump will be impeached. Others based in the United Kingdom are drawing bets on the less-specific question of whether Trump remains in office until his term expires in January 2021.
The contract on PredictIt titled "Will Donald Trump be impeached in 2017?" saw volume of more than 100,000 contracts in the last 24 hours after reports of a memo written by Comey that said Trump had asked him to end the Federal Bureau of Investigation's probe into ties between former White House national security adviser Michael Flynn and Russia.
At one point early on Wednesday, the price of a "yes" contract on the impeachment question jumped to a record 33 cents, implying a 33 percent probability that Trump would be impeached. That compares with only 7 percent just over a week ago.
By late in the day, however, the price had slid back to 27 percent, just above where it ended late Tuesday at 24 percent.
PredictIt is jointly run by Washington political consultancy Aristotle and Victoria University in Wellington, New Zealand. All of its users are registered U.S. voters.
The bookmaker Paddy Power Betfair (PPB.I) (PPB.L) said bettors there had laid out more than 5,000 pounds ($6,470) on an early departure for Trump in the hours after it was reported Trump had asked Comey to shut down the FBI's investigation of Russia ties.
In all, the question of whether Trump will make an early exit has drawn more than $270,000 in wagers, while a related question on whether Trump will leave in 2017, 2018, 2019 or 2020 or later has garnered more than $480,000.
British betting firm Ladbrokes (LCL.L) cut the price of a Trump impeachment to odds-on at 4-5 from 11-10, equivalent to about 56 percent probability that Trump will be removed from office.
"Political punters are wondering how many more scandals can Trump overcome," said Ladbrokes spokeswoman Jessica Bridge.
"And despite the short price on offer, money has poured in for the president to be impeached, leaving us with little option but to cut the odds."