It took five years of intense negotiations and political controversyand last week, trade diplomats finally gathered in New Zealand to sign the Trans-Pacific Partnership (TPP) free trade agreement.

Now comes the hard part: The politicians still must approve it.

The signing on February 4 was merely a ceremonya necessary formality, but only a single step on the long road to TPPs enactment.

The massive trade deal involves a dozen Pacific-rim nations whose combined economies contribute more than one-third of the worlds total output. The U.S.-based Peterson Institute for International Economics says that over the next decade, TPP could boost global incomes by nearly $300 billion per year.

So far, however, only Malaysia has ratified TPP.

Almost everywhere, the deal has fallen under sharp scrutiny. At the ceremony in Auckland, protestors greeted the signers with outrage, shutting down the central city.

In the United States, top presidential candidates have savaged it. The two major Democratic candidates, Hillary Clinton and Bernie Sanders, oppose TPP, even though President Barack Obama, also a Democrat, has called for its passage.

On the Republican side, Donald Trump blasted TPP in a debate on Saturday night: It is going to be a disaster, he said. Three days later, he won his partys primary in New Hampshire. The winner of the Republican caucuses in Iowa, Ted Cruz, is a foe of TPP as well.

Most Americans say that trade agreements have been good for the United States: 58 percent, in a Pew Research Center survey last year. On the campaign trail, however, it would appear that protectionism is popular.

Here in New Zealand, we expect a pitched battle over TPP. As an island nation, were an outward-looking country. We produce high quality food, with an emphasis on ethics and environmental sustainability. My own farms focus on seed production and dairy farming on the South Island, New Zealands larger but less populated island.

All of us New Zealanders depend on our ability to trade with other countriesand TPP will give us better access to 800 million middle-income customers, eliminating tariffs on 93 percent of our exports.

TPP will improve our ability to buy and sell with the United States and Japan. The agreement is the equivalent of opening new storefronts in the worlds largest and third-largest economies. In addition were looking forward to better economic relations with Canada, Mexico, and Peru, which are also TPP signatories.

The benefits are mutual. Just as well sell more to Americans and others, theyll sell more to us. I dont know that TPP will add many jobs to New Zealands economy, but it may change the jobs we do, as we constantly learn new skills, create new and more products and discover new ways to help each other.

I think people should feel immensely proud of TPP and actually excited by the opportunity it presents, said John Key, New Zealands prime minister, shortly before last weeks signing.

Yet many Kiwis are concerned about that lack of information that surrounded TPPs negotiations. They worry that it will raise the cost of medicine and hurt the environmentand that it may even limit our sovereignty, giving foreign governments greater powers to challenge our laws and sue us.

Our current government supports TPP, but opposition parties are against itand anything could happen.

Some countries want the United States to move first: Theyre waiting to see when President Obama will submit TPP for legislative approval and whether Congress even will approve it. This years elections complicate everything.

Yet I believe that TPP will advance with or without the United States. If Americans decide to turn away from TPP, then the nations of the Pacific Rim may begin their own pivot to Asia, building new relationships and alliances.

By rejecting TPP, the United States would miss out on economic opportunitiesbut perhaps more regrettably, it would surrender its leadership position in the region.

That would be the biggest failure of all.