Opposition Democrat lawmakers have ramped up calls for an independent investigation into possible collusion between the Trump campaign and Moscow since Trump's surprise firing of the head of the Federal Bureau of Investigation on Tuesday.
The shocking news drew immediate comparisons to former President Richard Nixon's dismissal of the independent Watergate investigator Archibald Cox in 1973. Nixon resigned the following year after a congressional panel voted for impeachment.
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By Wednesday, the odds for a Trump impeachment during his first term had risen from 2/1 to 4/6, representing a 60 percent chance, according to Lewis Davey, a spokesman for the Irish betting site Paddy Power.
"We can attribute this to the news of Comey's sacking," said Davey, adding that the current four-to-six odds were "the shortest we've been for Trump to be impeached in his first term."
Online gambling is still largely prohibited in much of the United States and so the odds likely do not reflect a significant share of American views.
The betting odds are also not probabilities for any outcome -- but do reflect the weight of money that punters have staked.
Naomi Totten of Betfair, a separate British betting platform owned by the same corporate parent as Paddy Power, said the Comey firing had customers eager to wager on a Trump downfall.
"There's someone who's looking to place a hundred thousand pounds on Trump to leave," she told AFP, a sum currently equal to about $129,000.
The unnamed gambler had already staked 30,000 pounds and was seeking to add another 70,000, but no one had so far taken that bet, Totten said.
In the hours following Comey's ouster, the odds that Trump will leave office before the year is out went from 9/1 to 3/1, according to Totten.
Since Comey's firing, bets have been lighter on whether Trump will leave before the end of his first term in January 2021, she said, "but they have been big enough to move the odds from 15/2 to even money."
The president's poll numbers have reached near record lows since his inauguration and the president's favorable rating is currently at 54.2 percent, according to the Real Clear Politics average of polls.
Trump's Republican party controls both chambers of Congress, reducing the likelihood of an impeachment.
