Two months ago, the Betfair odds implied there was a 10% chance that the Next President would be somebody other than Donald Trump or Joe Biden. Despite no challenge materialising to either and the latter securing a majority of delegates to become the presumptive Democrat Nominee, that combined estimate is still 8%, inching higher at moments in yesterday's trading.
The big mover is Mike Pence, upon reports that Trump might withdraw from the race. The Vice President has more than halved in odds from [140.0] to [60.0], trading down to [50.0] yesterday. Hillary Clinton, Nikki Haley and Kamala Harris have also notably shortened of late.
2020 betting may be even crazier than 2016
Bizarre as it may sound, this is actually quite normal for a US election. In 2016, Biden, Pence, Bernie Sanders and Paul Ryan generated large trading volumes even after both parties had confirmed different candidates.
The day that Hillary Clinton collapsed with pneumonia in Manhattan remains the most surreal and dramatic I can ever recall in political betting. Closely rivalled by the 72 hours following the release of the 'Pussygate' tapes that so many of us thought had finished Trump, which prompted Wikileaks to release the John Podesta e-mails.
Given how fake news and confected scandals are even more prevalent now, expect similar drama in 2020. There is bound to be at least one attempt at an 'October Surprise'. That, however, seems a long way from what could be a ruinous July for Trump.
Pence moves make sense with Trump on ropes
For once, I think there is real substance behind this gamble on Pence. Trump is in a world of trouble. On the ropes, facing a series of potential knockout blows.
There isn't anywhere near the space to cover all of Trump's scandals here. In short the last ten days have seen him sack the NY prosecutor investigating his finances, family and friends and John Bolton's devastating book reveal one foreign policy outrage or impeachable offence after another. The Supreme Court will rule imminently whether he must release his financial and tax records - including the infamous relationship with Deutsche Bank.
Then on Friday, arguably the worst emerged. Claims that Russia was paying the Taliban to kill US troops, yet Trump had yet to formulate any sort of response. Rather, he'd since campaigned for Russia to join the G7 and given them a huge foreign policy concession by removing troops from Germany.
Trump has so far denied being briefed on this intelligence - a defence that few experts find credible. The story appears to be confirmed by the range of media and intelligence sources. Literally as I write, Watergate journalist Carl Bernstein is on CNN, claiming that senior White House officials concluded Trump himself was a threat to national security.
My impression over the weekend is that the Trump machine is shellshocked. Their current position is unsustainable. If he was briefed, he must explain why no action was taken. If not, why not, and what is the response to be now he knows?
Trump withdrawal now an open talking point
Reports have also emerged that Trump is deflated, realising the terrible polls aren't fake and he might lose because 'some people don't love him'. That he is considering withdrawal. Significantly these reports don't come from opponents, but Fox News hosts and a close ally of Roger Stone.
It is almost two years since I predicted on these pages that corruption would finish Trump, forcing him to withdraw in 2020. Four years since I first discussed the threat from his relationship with Vladimir Putin. True, he has defied expectations, once in an election, twice in somehow managing to shake off the Mueller Report and imprisonment of numerous key allies.
Could it all be coming together? We are in uncharted territory. I have said from the outset that Trumpism was unsustainable. The next month - as this latest Russia story evolves, the Supreme Court rules and his niece Mary Trump publishes her damning book - may prove the tipping point.
I certainly feel it is worth keeping Pence and Nikki Haley onside at still attractive odds. The latter - a female, former UN Ambassador and South Carolina Governor - is much more electable. Republicans could plausibly decide she is a better bet with those pivotal white suburban women against Biden.
If withdrawal becomes likely without an obvious replacement, any number of huge-priced Republicans could come into the reckoning. Or GOP-leaning celebrities such as Mark Cuban or Dwayne Johnson.
Biden's VP pick bound to shorten
What of the Democrat side? I have no reason to think Biden won't be the candidate. There are no credible reports. Nevertheless, the Trump machine will persist in saying 'Sleepy Joe' is senile, and sharing edited footage to emphasise it. Expect some punters to continue to search for alternatives.
Clinton, as ever is both popular in the betting and ridiculously priced. She will not be the candidate. Even if Biden withdraws and the first five alternatives reject the offer. Nor will it be Bernie Sanders, although there might well be another gamble on him down from [390.0]. The very electable Andrew Cuomo's odds might crash again from [310.0].
If you want to look for an alternative to Biden, check the Democrat VP Nomination market. Whoever wins will be in pole position and may well trade down to [50.0] or lower. Hence the move for Harris. One with shortening potential is Susan Rice at [1000.0]. She's now second-rated behind Harris for VP at [8.4] and may rise further on the basis of recent trends.
Follow Paul on Twitter and check out his website, Political Gambler.