A potential President Donald Trump would be almost as painful for Asia as for his usual whipping boy, Mexico, Nomura has warned.

"A Trump presidency would no doubt hurt Asia's gross domestic product (GDP) growth and could ultimately drive cost-push inflation, impart smaller trade surpluses and looser macroeconomic policies," Nomura said. "South Korea and the Philippines would be among Asia's most vulnerable in terms of both economic and geopolitical channels, while India and Thailand seem among the least exposed."

Nomura noted that it wasn't making any predictions on the eventual winner of the presidential election.

But the bank noted that assessing the actually impact would be "tricky."

"Trump has no track record as a policymaker, while his economic nationalism and campaign bravado has made for unclear and sometimes inconsistent statements or stances on key issues," it said. "This makes it particularly hard to confidently predict what he would actually try to do, let alone be allowed to do, by America's system of checks and balances should he win the presidency."

Protectionism, threats to national security and uncertainty over U.S. macro policy were the key risks, Nomura said.

Trump's threats to undermine existing trade deals, such as NAFTA, or raise tariffs, were a key concern, Nomura said.

"While Mr. Trump has threatened trade barriers against Mexico, Japan and China, the knock-on effects from China – the world's largest manufacturing assembler – to other Asian countries that are major suppliers of high value-added parts and components to China would be substantial," it said.

Additionally, while Trump had pledged to increase the U.S. military presence in Asia, he had also claimed he could force U.S. allies to pay the full cost of security guarantees, Nomura noted. If attempts to squeeze significant financial contributions out of Japan and South Korea fail, Trump may cut back on the regional U.S. military presence or close U.S. bases entirely, Nomura expected.

"Even a partial U.S. military withdrawal would likely embolden Beijing to pursue its current assertiveness in the South China Sea," it said.

Additionally, withdrawing U.S. forces from South Korea would dramatically alter the balance of power on the Korean peninsula even as the North was closing in on long-range nuclear capability, Nomura noted.

Removing U.S. troops from Japan could also spur Prime Minister Shinzo Abe to step up efforts to change the country's constitution and strengthen its military capability, which could increase the potential for open conflict in the region, Nomura noted, citing analysis from Alastair Newton, director of the bank's geopolitical consultancy Alavan Business advisory.