President Donald Trump pauses as he talks to members of the White house travel press pool on board Air Force One during his flight to Palm Beach, Florida while over South Carolina, Feb. 3, 2017. REUTERS

A leading British betting house has put even odds on the prospect of President Donald Trump resigning or being impeached before the end of his first term. The odds were set amid questions swirling about the president's administration having ties to Russia in the wake of the national security adviser's resignation.

Ladbrokes has listed odds that Trump will "leave office via impeachment or resignation before end of 1st term" as "evens," meaning the betting house believes there is a 50 percent chance Trump will quit the presidency or be forced to leave it through impeachment by Congress. The site was giving 4/5 odds that Trump would serve his full term, meaning the betting house thinks there is a 55 percent chance Trump was still president Jan. 20, 2021. (Trump could be impeached and still complete his term, a possibility that explains the different odds for the two bets).

The site was also taking bets on the timing of Trump potentially being replaced. While 2021 was the current favorite choice, with 2/1 odds, the second-most likely outcome was that Trump will be replaced this year, Ladbrokes calculated. The site was giving 5/2 odds Trump will be replaced in 2017.

Other British betting sites were slightly more optimistic Trump would complete his first term. Bovada gave the president a 58.33 percent chance of completing his first term, but that was down from the 73.3 percent chance it gave him just last week.

While impeachment seems very unlikely with Republicans controlling both houses of Congress, Democrats drew parallels Wednesday between Trump and the scandal that took down Richard Nixon, the only president ever to fail to finish a presidential term for reasons other than death.

"This is already bigger than Watergate," said a statement on Michael Flynn's resignation issued by the DNC.

Both Andrew Johnson and Bill Clinton were impeached by the House of Representatives, but were acquitted by the Senate, which allowed them to finish their terms. No president has ever been forced out of the White House by impeachment. Nixon resigned the presidency in 1974.

Trump's tumultuous first weeks in office have created new interest in political betting markets, Ladbrokes said.

“From a betting perspective, Donald Trump’s presidency has triggered a massive boom for these kinds of markets,” said Alex Donohue, the PR manager of Ladbrokes told Politico. “With Donald Trump, everything he does, it can be turned into speculation, and that can be turned into gambling.”