Where the polls stand on the eve of the first US presidential debate

UPDATE: The latest polls show Hillary Clinton and Donald Trump both upo slightly at the expense of the third-party candidates. The most significant battleground state development is that Mrs Clinton has pulled ahead in Florida, where she now leads by an average 0.5% thanks in part to a Reuters IPSOS poll released this morning that has her up 49 to 45 — but it's still margin-of-error stuff.

All the numbers below are updated for midday Tuesday NZT, the eve of the debate.

The US presidential race is achingly close going into the first US presidential debate, to be held in New York 9pm Monday (2pm Tuesday NZ time).

A New York Times poll-of-polls has:

• Hillary Clinton: 45%
• Donald Trump: 42%

Or, with Libertarian candidate Gary Johnson factored in (the Times is not tracking Green candidate Jill Stein):

• Clinton: 43%
• Trump: 41%
• Johnson: 8%

The RealClearPolitics’ poll-of-polls has:

• Clinton: 46.6%
• Trump: 44.3%

Or with the third-party candidates included:

• Clinton: 43.1%
• Trump: 41.5%
• Johnson: 7.4%
• Stein: 2.4%

On FiveThirtyEight, Nate Silver – still widely regarded as a stats guru, despite muffing his Brexit prediction – gives the Democrat (as I type) a 54.8% chance of winning.

Comes down to the swing states
The US system, which allocates states Electoral College votes based on population, mostly on a winner-takes-all basis; 270 Electoral College votes are needed for a majority (and it does all come down to the Electoral College; in 2000, Al Gore won the popular vote nationally but George Bush won the White House as he squeaked over the line in Florida). The winner of the biggest state, California, claims its 55 Electoral College votes; the winner of the smallest, Wyoming, takes its 3 votes and so on. Here's how the race looks right now according to FiveThirtyEight's Electoral College forecast map, which draws on state-level polls to give Mrs Clinton 284 Electoral College votes to Mr Trump's 254.

The two largest battleground states are Florida (29 electoral college votes), where RealClearPolitics says Mrs Clinton has an average poll lead of 0.5%, and Ohio (18 votes), where the Republican has an average lead of 2%

If Mr Trump were to win Florida (still within the margin of error and inside his camp according to FiveThirtyEight) and Ohio, he still needs to take Colorado (where Clinton leads by 1.5%) or two smaller states to get to the magic 270 Electoral College votes. As a FiveThirtyEight graphic niftily displays it:

Click to zoom.

Mrs Clinton’s slim lead seems to have survived her initial secrecy over her pneumonia diagnosis, her buckle on 9/11 and the Chelsea bombing that, on the face of things, should have played into Trump’s hands as he tries to be the strong man on terror.

The Republican has largely maintained his more disciplined approach but has been undermined to a degree by a Washington Post expose on his charitable foundation. Following a detailed investigation, the paper says Mr Trump used $US258,000 from his non-profit to settle lawsuits involving a number of his for-profit businesses.

Mr Trump has called the Post biased and accused it of going soft on the Clinton Foundation (more on which here), but has yet to rebut the central elements of its story.

Debates can be decisive
Televised debates can swing presidential elections.

In the tight 1960 race, TV viewers thought a sweating, light-suited Richard Nixon looked shifty, while radio listeners who were also polled thought he had got the better of John F Kennedy (TV viewers were derided at the time for being superficial, though of course history proved their instinctive reaction correct).

In 1992, George HW Bush cast an anxious glance at his watch. He later said he was merely keeping time. Viewers' verdict: he couldn’t wait for his contest against Bill Clinton to be over.

The four 2016 debates will see a clash of styles.

Mrs Clinton is a famous swot but Mr Trump favours sweeping generalisation over policy detail, giving her little in the way of specifics to dispute.

Presidential debates are also an expectations game.

In 2000, George W Bush set the bar so low that he drew praise simply for being able to string sentences together. Al Gore was hyped as a debate master but came over smug.

Mr Trump affects to have done little debate preparation and says the moderators chosen by the independent commission that runs the debates will be biased (he said one, NBC Nightly News anchor Lester Holt was a Democrat; in fact, Mr Holt is a registered Republican). In part, he’s playing the Bush Jr expectations game but his lack of homework also risks a “What’s Aleppo?” moment a la Gary Johnson if he’s pressed for domestic or foreign policy knowledge.

The risks
Mrs Clinton’s performance is largely predictable: She’ll be a little wooden, a little patronising, but also well drilled on policy, and rehearsed on how to react if Mr Trump tries to taunt her. The only real question will be whether her pneumonia affects her performance.

For Mr Trump, it’s not so much a question of whether he says something outrageous (over four 90-minute debates, the chances of avoiding a doozy are zip), but whether the electorate sees him going over the line or being refreshingly maverick. Things could turn on how much moderators press him to justify his more outlandish statements.

Timetable from here (US dates)

• First debate: September 26
• Second debate: October 4
• Third debate: October 9
• Fourth debate: October 19
• Election: November 8

Gary Johnson and Jill Stein won’t participate in the debates, having failed to reach the commission’s threshold of 15% support across four major polls.

The other key question is whether the Republican Party will maintain its majority in the House and majority in the Senate. As things stand, it's looking likely to hold both houses of Congress.

Congress controls the purse strings and a Republican-dominated Congress could be equally hostile to a President Trump or President Clinton. And this is against a background of fiscal constraint; according to a Wall Street Journal analysis, the next president could have less room to cut taxes or raise spending than anyone occupying the Whitehouse since World War II.