Nomura: This region would be hurt most by a President Trump

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.

Nomura also cited concerns that a President Trump would follow through on his plans to cut corporate and personal taxes, which would increase the budget deficit sharply over the next 10 years, hurting U.S. fiscal sustainability. The bank was also concerned about indications from Trump that he would "restructure" U.S. government debt, which would likely spur Asia's central banks to scale back their Treasury (US10Y) holdings, causing sharp moves in bond prices and exchange rates.

But when it came to playing the impact in the market, Nomura noted its forecasts were subject to some caveats.

"How financial markets should prepare for a 'known unknown' going wrong is far from clear," it said.

But it expected that China's currency would fall further if a hypothetical President Trump aggressively pursued his stated policies against the mainland.

Nomura also expected the South Korean won (KRW=) would weaken on a less favorable trade environment with the U.S. and greater political uncertainty on the Korean peninsula.

But Indonesia's rupiah (IDR=) and Malaysia's ringgit (MYR=) could perform better, bolstered by strong domestic demand, strong bond inflows and relatively positive political and policy developments.

For stocks, Nomura expected that the region's listed defense contractors would benefit due to rising military tensions and risks of confrontation.

The bank also liked defensive stocks in Thailand and Malaysia as they would be among the Asia markets most insulated from a Trump presidency.

Yield stocks would also likely outperform, Nomura said.

"To the extent that a Trump presidency contributes to further growth downgrades and downside pressure on global yields … we also continue to favor higher-yielding stocks (like REITs) and exposure to precious metals," it said.

Nomura expected that Chinese exporters to the U.S. would underperform on potential tariff hikes and that Indian information technology companies would face headwinds from a potential crackdown on U.S. visas for their workers.

South Korea's automakers could also take a hit if Trump were to interfere with the country's current free-trade agreement with the U.S. and as the companies have an extensive presence in Mexico to take advantage of NAFTA.

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—By CNBC.Com's Leslie Shaffer; Follow her on Twitter @LeslieShaffer1