It's only July and yet 2016 is already being discussed as one of the worst years ever. On Monday things may have become a little worse: American opinion polls are now putting Donald Trump ahead of Hillary Clinton in the race for the US presidency for the first time. All six national polls are giving Trump a victory over Clinton.

The CNN/ORC poll, for example, predicts a three-point lead for Trump over Clinton in a head-to-head race, while FiveThirtyEight's Nowcast – which estimates who would win if the election were held right now – also has the Republican candidate taking home the presidency.

Caveats abound.

First off, the spike in Trump's numbers comes on the back of the Republican National Convention where he was officially named the party's presidential candidate. Pollsters say that candidates traditionally get a "convention bounce" in the polls, since likely voters who might have supported others in the same party rally behind the official nominee. In Trump's case that bounce is as high as 6 points, in the CNN poll.

Secondly, the Democratic National Convention is just beginning and will run through the next few days. Clinton could end up benefiting from the same effect, seeing her own poll numbers bounce up and beyond Trump's to re-establish her lead.

And thirdly, it is still only July. The election is not until November, and FiveThirtyEight has established that polls don't become properly predictive until about 30 days after the conventions. As Vox shows, even Republican candidate John McCain took the lead over then-candidate Barack Obama after the Republican convention in September 2008, before losing the election later that year.

Except even that approach has one problem: It shouldn't even have been this close in the first place.

Conventional wisdom would suggest that the numbers ought to be on Clinton's side. This takes into account the fact that much of the Republican party still seems divided over Trump and Clinton has just picked a vice-presidential candidate that bolsters the governance bona fides on her ticket, a clear contrast to Trump's barely comprehensible, often blatantly untrue and sometimes truly scary policy positions.

Numbers in June, when it became clear that both Clinton and Trump would be candidates, made it seem as if the Democrats would win in a landslide. That lead has now become much tighter.

There was a belief in the Clinton camp that Trump's nomination, including the complete mess that was the Republican convention – with a plagiarised speech and a non-endorsement – would play up the differences between the tickets. Instead, the Democrats have started on an equally bad note.

The convention was supposed to display the Democrats unity, in contrast to Republican disarry. Then WikiLeaks released 20,000 emails showing that DNC staffers favoured Clinton over competing candidate Bernie Sanders, forcing the convention's chairperson to resign, and leaving a cloud over the entire event. The emails could threaten the truce that had been brokered between Clinton's camp and Sanders supporters, and hurt the candidate even more.

Clinton could still come back from this with a strong showing through the rest of the convention. But the fact that Trump has taken the lead will come as a shock, and one can never underestimate the Democrats ability to mess things up for themselves.

The polls are also a good reminder of the rest of the world, especially in foreign capitals where Brexit was seen as an extremely unlikely outcome: A Trump Presidency is a real, serious and scary possibility. Brace yourselves.