WHITE HOUSE - Rhetoric on the U.S. presidential campaign trail has left many in the Asia-Pacific region wondering whether America's commitment to economic growth and security in the region will survive into the next presidency, regardless of who wins.

In a campaign marked by caustic, tawdry and highly personal remarks, one candidate has threatened to withdraw the U.S. nuclear umbrella that protects countries like South Korea and Japan, while both have opposed a landmark trade deal seen as the linchpin of the region's future prosperity.

The campaign "has really undermined the faith and the convictions that many regional actors have about the viability of American commitments [and] the stability of our own democracy," said Jonathan Pollack of the Brookings Institution's Center for East Asia Policy Studies.

US must 'tap into' Asia-Pacific

American leaders are necessarily preoccupied by the high-profile conflicts in the Middle East and the threat to the homeland posed by Islamist terrorists. But analysts point to looming threats in the Asia-Pacific, a region that accounts for almost 40 percent of world output, according to the International Monetary Fund.

Chinese ship and helicopter are seen during a sear
FILE - Chinese ship and helicopter are seen during a search and rescue exercise near Qilian Yu subgroup in the Paracel Islands, which is known in China as Xisha Islands, South China Sea, July 14, 2016.

North Korea has ramped up nuclear and missile tests in the Korean Peninsula, tensions have mounted over China's territorial claims and aggressive actions in the South China Sea, and the new president of longtime ally the Philippines has vowed to "break up with America" and turn to China as its main ally.

Both former President George W. Bush and President Barack Obama worked to open diplomatic, security and economic channels in a bid to cement America as a leader in the Asia-Pacific, where China is rapidly amassing power and influence. U.S. military assets in the region have been growing since Obama promised a "pivot to Asia" early in his presidency.

Statements by Republican presidential nominee Donald Trump and Democratic presidential nominee Hillary Clinton, however, have left many in the region wondering whether that commitment will continue.

Trump, in particular, has alarmed long-time allies by suggesting he no longer would guarantee the defense of South Korea and Japan unless those countries contributed more to the cost. He also has vowed to kill off the 12-nation Trans-Pacific Partnership, a ground-breaking trade treaty designed to open markets around the Pacific Rim.

A delegate holds an anti-Trans-Pacific Partnership
FILE - A delegate holds an anti-Trans-Pacific Partnership (TPP) trade agreement sign during the first day of the Democratic National Convention in Philadelphia, July 25, 2016.

There is "fear and loathing" in the Asia Pacific about a potential Trump presidency, said Robert Manning of the Atlantic Council's Brent Scowcroft Center on International Security. This feeling, Manning added, comes even though there is "not enough coherence to Trump's comments" to be certain what he might do once in office.

Clinton, Trump both oppose TPP

Clinton would be expected to continue the Obama administration's strategic rebalance, but she has been emphatic in her rejection of the TPP, which is opposed by unions and blue-collar workers whose support she needs. Without an economic commitment in the region like TPP, U.S. credibility is lost, experts say.

During an economic address three months ago in Warren, Michigan, Clinton said of TPP: "I oppose it now. I'll oppose it after the election, and I'll oppose it as president." She had previously expressed support for the trade partnership.

Pollack, the Brookings Institution analyst, said Clinton has softened her language in some recent statements, and "seems to be trying to create a bit more space, a bit more flexibility."

An adviser on Asian issues who worked with Clinton at the State Department gave a similarly nuanced description of her position during a discussion at the Korea Economic Institute in Washington.

FILE - Former U.S. secretaries of state meet with
FILE - Former U.S. secretaries of state meet with President Barack Obama to discuss the Trans-Pacific Partnership at the White House in Washington, Nov. 13, 2015.

"She cannot accept the trade agreement, TPP, as it's currently being negotiated," said Kurt Campbell, a former assistant secretary of state for East Asian and Pacific affairs under Clinton. "At the same time, she also recognizes that some form of commercial engagement will be necessary going forward."

It is Trump's comments on regional security, though, that are causing the greatest anxiety.

Trump's cynicism about alliances

During an August rally in Des Moines, Iowa, he expressed frustration about Japan, one of America's closest allies. He told supporters Japan cannot help if the U.S. is attacked because its constitution bars overseas military action.

"If we're attacked, Japan doesn't have to do nothing," said Trump. "They can stay at home, watching Sony television, right?"

The Pacific nations in fact contribute significantly to regional defense, particularly against the threat posed by North Korea. Japan pays $1.6 billion a year in host-nation support for U.S. military operations in Japan, and South Korea pays almost $1 billion for the same reason.

Manning argued that Trump's approach suggests a lack of understanding "of the whole post-Cold War, rules-based order that U.S. leadership has been essential in enforcing."

But Trump adviser Peter Hoekstra, a former U.S. congressman, said the candidate recognizes the United States must invest in its role as a global leader, although "there are responsibilities to American taxpayers and American workers."

"It's time to go back and start from ground zero and do a full assessment of what our strategy needs to be to confront the challenges that are out there," Hoekstra said during the discussion at the Korea Economic Institute. "It doesn't mean to ... challenge the relationships or the friendships that we have in Asia."

Pollack said the economic, security and diplomatic importance of the region is too great for any president to ignore. "It's inconceivable to me," the Brookings Institution analyst said, "that any American president will, in fact, try to detach the United States from the region."