President Barack Obama decided to come out in the third debate and attack. And the instant polls on the US TV networks gave him the win by some considerable distance.

Mitt Romney's approach was considered although, certainly in the early stages, markedly less confident than in the two previous contests.

Opinion polls rate him higher on the economy and so his task in this debate on foreign affairs, was to link everything back to the situation at home.

He also spent a lot of time agreeing that what Barack Obama had done and was doing was right. This was a calculated step.

Not only does it subtly attach the Republican hopeful to the higher approval rating his opponent enjoys on the handling of foreign affairs, it works in with the continuing shift to the political centre he began in the first debate in Denver at the beginning of the month.

This was a Mitt Romney more concerned about peace than war. A Mitt Romney who has 19 advisors on foreign policy who worked in the two previous Republican administrations, yet insisted he did not want "another" Iraq. A Mitt Romney who wanted to show America, weary of 11 years of conflict in Afghanistan and still counting the cost of the bloody invasion of Iraq, that he was not about to drag them into yet another foreign war. This was a less hawkish version of the candidate who battered his way through the primary process insisting Israel had "no greater friend".

The lines of the night perhaps belonged to Barack Obama, and on such things wins and losses are often judged. On Romney's desire to increase military spending, worried that the navy was understrength, he responded a touch mockingly "You mentioned the navy, for example, and that we have fewer ships than we did in 1916. Well, governor, we also have fewer horses and bayonets because the nature of our military's changed". This is the line that will be constantly replayed - and so for those who did not watch, it will be the defining memory of this contest, and as such, a good moment for the president.

In response to Romney's earlier assertion that the US' biggest geopolitical foe was not al-Qaeda but Russia, Obama brought laughter to the press room with his retort: "The 1980s called, they want their foreign policy back".

Mitt Romney retained his poker face, the fixed, slightly smiling expression in response. Democrats insist it was because he had no answer. Republicans believe their man came over as calm, in control and well presidential.

Many issues were not covered. There was no mention of a peace deal in the Middle East between the Israelis and Palestinians. Climate change and the danger to the planet was not raised once, emphasising again how it has simply disappeared from the international agenda. There was no discussion of the drug wars in Latin America and no mention of the issues confronting sub-Saharan Africa. Foreign policy for the two candidates revolves around Iran, the wider Middle East, Afghanistan and occasionally China.

There is a danger for Mitt Romney in this performance in Florida. His new moderate positions are clearly different from those pushed by candidate Romney in the primaries, designed to appeal to moderates, undecided and disaffected Obama supporters. Yet, it opens him to the charge of once again flip-flopping or even "etch-a-sketching" on important issues.

Tellingly both men at points, hijacked the debate from the moderator, dropped the conversation on foreign policy and turned instead to the economy which remains the issue which most concerns Americans.

It is the area which clearly highlights the differences between the two men, more so than foreign policy.

And ultimately, it will be the economy that decides this close election.