The most obvious and immediate impact of yesterday's first US presidential debate was to make Democrat Hillary Clinton look like a confident, competent winner again before many millions of possible voters.

That's something that hasn't been the case since August's Democratic National Convention, which resulted in a lengthy poll bounce both nationally and in the battleground states.

Clinton's performance will have come as a huge relief and boost to Democrats and may have inspired some waverers considering Republican rival Donald Trump or third-party candidates to think again.


It felt like a reset that stalled her opponent's momentum.

The key question now is whether this performance actually results in Clinton pushing beyond her 2 to 3 point national poll lead of September and improving her position in swing states.

The fact that she was able to dominate at her first appearance with Trump was also significant.

Debates are about moments, impressions and outlines that stick in the memory. Seeing the pair together on the same stage as direct rivals and with no distractions, amplifies their qualities and differences.

Yes we've seen angry, divisive Trump; soundbite and showbiz Trump; rambling, buffoonish Trump at various times in news clips and at the Republican National Convention.

But we've never previously seen him throw his best shot and then gradually get taken down through a series of hard jabs.

During the Republican primary season, Trump was able to pursue a strategy of punch and pause in debates, because of the large number of candidates.

The format here allowed Clinton to bait the bear, survive the first furious messaging hit and then skewer Trump on his business practises, tax returns, birtherism, women and race relations.

She drew the Republican into damaging replies, on federal income taxes and the housing crisis, at odds with his positioning as the bruiser for battlers.

CNN's Brian Stelter, in a tweet on preliminary viewing numbers, noted: "Important detail: there was no dramatic ratings drop-off between 9 & 10:40pm. Viewers were glued to entire #debate". Meaning most viewers saw the entire splatter.

It started with a jab at Trump's pride and legend of being a self-made man.

We learned that Trump was psychologically incapable of resisting a challenge to his ego and persona and was capable of spraying verbal own-goals in reply.

The truly damaging sting was that it fed a narrative about Trump that even his supporters fret about.

The top concern of 34 per cent of Trump's backers is their candidate's temperament and unpredictability, according to Pew Research Centre data.

In fact, while Trump showed he can flick a switch from calm to aggressive in an instant, he is entirely predictable about defending his Achilles' heel - his precious reputation.

Trump's most effective period came in the first half hour when he hammered Clinton on trade, jobs and being a career politician, he charged, only now coming up with plans to fix problems.

His simple slams will survive what followed and Clinton will need better answers in the later debates. She squirmed over her stances on TPP.

Republican presidential nominee Donald Trump kisses his wife Melania. Photo / AP
Republican presidential nominee Donald Trump kisses his wife Melania. Photo / AP

But even there, a viewer's response to Trump's hulking barks at Clinton on trade might be largely different according to gender. Women voters may have been less impressed with his tone and manner than men - numerous comments on social media suggested so.

For much of the debate, Clinton showed she was prepared, knowledgeable and relaxed enough to come across as likeable and presidential, helping Trump stumble into silliness - "I have a great temperament" - while making callouts to the Democratic coalition of liberals, minorities and young voters. She dealt with her email saga simply and clearly.

She lobbed a news grenade into Trump's lap in the form of his alleged treatment of former Miss Universe Alicia Machado.

Clinton skated close to potential danger in her obvious derision for Trump and what some would see as touches of smugness. Remember Al Gore was reckoned arrogant for being dismissive of George W. Bush in 2000. However, Clinton was shielded from much negative impact in that regard by comparison with Trump's own regular interruptions and reactions.

Nothing Trump did or said is likely to shake his really hardcore supporters. But it is difficult to see how he was able to expand his base, which is his key problem. Trump is likely to at least be better prepared for the next debate, but Clinton must feel confident she has his measure.

Currently Clinton's national average poll lead according to is +2.4. She has inched ahead in Florida but Pennsylvania and Colorado - two key states in her firewall - have suddenly become vulnerable.

Should the debate result in movement in the polls towards Clinton, she will concentrate on avoiding any damage in the subsequent encounters.

That's a front-runner's strategy.