Traders are not calling the election one way or another at this stage, but the reaction shows there is now greater uncertainty about which way the result will go on 8 November.
Even ABC News and the Washington Post, who commissioned the bombshell poll that gave Mr Trump 46 per cent of the vote to Hillary Clinton’s 45 per cent, would not say this shows the Republican is more likely to become President.
And that’s not just because the gap is well within the poll’s margin of error of three percentage points.
The US election will be decided not by national voter preferences. Instead, the result will be decided on a state-by-state basis, with all of each state’s electoral votes going to the candidate who wins the popular vote within that state.
That means the election will be decided not by simply who gets the most votes across the nation, but by who can secure even the narrowest victories in key swing states.
If we look at the picture across the US provided by polling resource website Real Clear Politics below, we see that many states can already be categorised either as leaning or very likely to go for either Trump or Clinton.
The state of play
Based on these states alone, the Democrats have a sizeable lead of 259 electoral votes to the Republicans’ 164.
If we isolate the 10 swing states, where the latest polling gives either candidate a lead of fewer than 5 percentage points, we can see where the remaining 115 electoral votes are up for grabs.
Where it will be decided
From west to east, the states to watch out for on election night are Nevada, Arizona, Colorado, Iowa, Ohio, Georgia, Florida, North Carolina, New Hampshire and Maine.
Real Clear Politics also keeps tabs on the latest polling within each of these states, ranging from Clinton 4.7 points ahead in New Hampshire to Trump 4 points ahead in Georgia.
If we believe the latest state-based polling, filling in those swing states gives five to each candidate - and a solid overall victory to Ms Clinton.
State-level polling gives Clinton a clear win
But what happens if Mr Trump takes all those swing states - even the ones where he is trailing nearly 5 points in local polling?
That gives Mr Trump 279 to Ms Clinton’s 259 - in effect, taking him over the line of 270 electoral votes required for victory.
Red across the board
How likely that is depends on how much the vote tightens in the final days, as US elections tend inevitably to do, and whether Mr Trump can translate his slight gains over the past week into a major boost on election day.
It also depends on how you define the swing states. ABC News’ own analysis names only five states as close enough to be a “toss-up” - Utah (which RCP has as leaning Trump), Arizona, Florida, North Carolina and Ohio.
ABC says Trump would still be 11 votes short of victory if he took all of these states - and would still need to “flip a blue state” to win.
The odds, in other words, still very much favour a Clinton victory. Moody’s Analytics, which has correctly predicted the last nine contests, actually forecasts Ms Clinton to pick up 332 electoral votes against 206 for Mr Trump.
Some - no least those jittery stock market traders - have compared the current approximately 75 per cent to 25 per cent odds of a Clinton win to the late-stage odds of a win for Remain in the EU referendum.
But with the future of the US decided by electoral colleges and not a straight national survey, Mr Trump has more work to do if he is to repeat a Brexit-style upset.
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