By Stephen Gibbs
BBC News, Guadalajara

The term "tres amigos" was coined by former US President George W Bush to describe the first North American Leaders’ Summit in 2005, held that time near his ranch in Texas.

The idea was simple: three North Americans, leaders of almost half a billion people, take time out to chew the cud, and shoot the breeze over how they can work more closely together.

There was a feeling then that the two presidents and a prime minister did not get to see enough of each other, and that a format needed to be found to make sure that in the midst of global distractions, the neighbours were not forgotten.

Four years on, one thing has changed. Summit or no summit, the three participants seem to spend plenty of time together.

To such an extent, that when they incessantly insist on describing each other as "my good friend", you almost believe them.

In the few months since being elected, President Obama has had six meetings with Prime Minister Stephen Harper, and five with President Felipe Calderon.

Drugs war

But there is a reason for all the face time. This region has three acutely pressing cross-border problems, which no country can possibly solve alone.

The first is the Mexican drug war.

At least six immensely rich and powerful drug cartels are fighting each other and Mexican government forces to retain control of what is possibly the world’s most lucrative business: shipping cocaine and other recreational drugs to the United States.

If ever there was a transnational problem, this is it.

In its simplest form it operates as follows: drugs flow north through Mexico; money and weapons flow south.

As the border between the US and Mexico is better policed, the traffickers explore new markets and new smuggling routes on the east and west coasts of Canada.

Total unity

It is a dangerous, intractable issue, but one in which publicly, the three leaders want to express total unity.

And so they did.

As they stood at their podiums alongside a neo-classical former home for destitute orphans, all were united in their support for President Calderon’s controversial hard-line against drug trafficking.

"I heartily compliment President Calderon and his government for their determination," said President Obama.

"We need to expand trade, not restrict it"

US President Barack Obama

Prime Minister Harper pointed to the "great personal risk" the Mexican leader had assumed by taking on drug cartels.

Earlier in the day a plot to kill Mr Calderon had apparently been uncovered by the Mexican police.

But behind the scenes it is more complex.

Mexico is frustrated that still it has received little of the almost $1.4bn (£0.85bn) in aid from the United States to battle the problem that has been promised.

Canada is worried that Mexico’s problem is becoming its own. It has recently toughened its visa requirements for Mexicans visiting Canada.

The policy is designed to control bogus visa applications, and ensure better control over who is entering Canadian territory.

Another vexing issue is swine flu.

The H1N1 virus is an enemy which the leaders did seem more comfortable uniting against in practical terms.

All signed up to a declaration promising to share information at every level regarding the disease.

It is seen as an inevitability that it will return to North America with a vengeance this winter.

Trade disputes

But the issue that is most sensitive for all three leaders is their intricately linked economies. The United States is the main trading partner of Canada and Mexico.

Its economic contraction has caused direct harm to the economies of both its neighbours, but most acutely that of Mexico, which sends 80% of its exports to the US.

Mexican assembly plants are finding that the business which expanded rapidly in the duty-free climate following the signing of the North American Free Trade Agreement (Nafta) can be switched off as quickly as it was switched on.

Auto exports are down almost 50% on last year. Cargo trade to the United States has also halved.

In the midst of this there are fears in Mexico City and Ottawa that protectionist voices in the US might be getting the upper hand.

Mexico says that a US ban on Mexican trucks operating inside the United States is inward-looking and counterproductive.

Canada has a similar position on the US decision to purchase from only American companies in its ongoing economic recovery programme.

President Obama attempted to be a voice of calm. "We need to expand trade, not restrict it," he said.

But no solution was offered for any of the individual trade disputes.

After deciding to skip lunch, the three amigos got into their respective planes, and left for their capitals. They vowed to see each other soon, at the G20 summit in Pittsburgh next month.

All know that the coming months will be difficult. And friendships will be tested.

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