Speaking in a panel discussion at the CEOs Summit at Apec in Lima, Key also revealed that New Zealand officials had done new modelling of the economic benefits to New Zealand if it went ahead without the US.
He said that showed it would deliver two thirds of the expected $2.7 billion annual benefit of the full TPP if the US dropped out but the remaining 11 countries implemented the current agreement.
That was because it would still deliver a trade agreement with four of the remaining TPP countries which New Zealand did not already have an agreement with - Mexico, Japan, Canada, Peru.
However, his preference was to keep the US in and he was "less negative" than many others about the chances Trump could be convinced to go ahead with TPP. He said Trump would be faced with the question whether he wanted the US to be a leader in the region.
Trump's election earlier this month put New Zealand exporters on edge.
Exporters are anxiously waiting to see whether Trump's rhetoric during the election campaign translates into policy, or whether his stance softens now that he has the top job.
Markets are unsure whether Trump will remain committed to his more extreme trade policies, including his pledge to leave the World Trade Organisation (WTO), withdraw from the North American Free Trade Agreement and impose significant tariffs on Chinese goods. NZ Institute of Economic Research's John Ballingall said ealier this month that all signs pointed to a trading environment that was less encouraging for Kiwi exporters.
"Certainly the ones I've spoken to are concerned about it, coming off the back of Brexit as well," Ballingall said. "Both of these decisions do point to a period of instability in global markets and to a global economy where trade liberalisation certainly won't be top of the agenda."
ManufacturingNZ and ExportNZ executive director Catherine Beard said the best-case scenario for New Zealand exporters would be that Trump's anti-trade views mellowed and the pro-trade factions of the Republican Party prevailed.
"The markets help keep governments honest and I'm sure there will be a lot of policy advice given to the incoming president to take sensible approaches to things, so let's hope that common sense prevails," Beard said.
The worst-case scenario would be the advent of an international trade war, she said.
