When Barack Obama visits Laos Monday, as part of what is likely to be his last trip to Asia as president, he will be cementing what many see as his most significant contribution to America’s “pivot” to Asia: strengthened relations with the Southeast Asian countries on the frontline of China’s assertive expansion in the region.

From the Philippines to Vietnam, Malaysia and Laos, Mr. Obama has strengthened US ties with the smaller countries in the region that are feeling the pressure of Beijing’s rise as an economic and military great power.

In some cases, most notably those of Burma and Laos, Obama has been instrumental in “flipping” once-closed and China-dependent countries to closer ties with the US and the rest of the world, many Asia experts say.

When historians “look closely at the so-called rebalance or pivot … the most significant legacy for the president is going to be engagement of Southeast Asia,” says Michael Green, senior vice president for Asia at the Center for Strategic and International Security Studies (CSIS) in Washington.

The reality is that the US rebalancing to Asia has been a continuing priority of US presidents since Richard Nixon, Mr. Green says. But he notes that Obama has significantly expanded leader-level engagement with Southeast Asian countries, building up military ties to a number of countries while establishing full diplomatic relations with Burma, also known as Myanmar.

“A lot of this has to do with China’s rise, but I think sustained diplomacy explains it,” says Green, a former director for Asian Affairs at the National Security Council under President George W. Bush.

Why TPP matters

At the same time, the weakest piece of Obama’s “pivot” – what Green dubs an “incomplete” – is the initiative’s economic dimension. In the eyes of most Asia analysts, the future of the US position in Asia and its role as a leader counterbalancing China’s economic rise depends on implementation of the Trans-Pacific Partnership.

Better known as TPP, it is a 12-nation Pacific Rim trade pact that Obama has vowed to pass in Congress before leaving office. But it faces strong headwinds in the US, notably from both major presidential candidates.

“The fact is, a lot of the Asian capitals where they have to constantly choose between bending to Chinese pressure or holding up Chinese pressure with American support are going to look to TPP as a sign of US long-term … staying power in the Asia Pacific region,” says Douglas Paal, director of the Asia Program at the Carnegie Endowment for International Peace in Washington.

“If TPP fails,” he adds, “the US will be seen as reducing its economic engagement [and] that over time the US will not maintain its military presence if it does not have an appropriate economic underpinning to it.”

The White House largely holds the same view. “If the US can’t complete the agreement, it would be seen as a significant setback, I think, for American leadership,” said Ben Rhodes, Obama’s deputy national security adviser, briefing reporters this week on Obama’s Asia trip. “We would be stepping back from that leadership role, we would be ceding the region to country like China who do not set the same types of high standards for trade agreements.”

Obama to meet with China's Xi

Obama arrives in China Saturday for two days of talks and a G20 summit, before moving on to Laos for bilateral meetings and two Asian summits. Obama will be the first US president to visit Laos and will participate in the US-ASEAN (Southeast Asian Nations) summit and the East Asia Summit – underscoring his commitment to the region.

In China he’s scheduled for a long sit-down with Chinese President Xi Jinping. Obama will hold a widely anticipated bilateral meeting with Turkish President Recep Tayyip Erdogan and is expected to meet on the G20 sidelines with Russian President Vladimir Putin.

For the White House, Obama’s last Asia tour will underscore what it sees as the president’s achievement: a “rebalancing” of US military assets and economic focus to Asia that allows for management of rising competition from an expanding China. Fortifying relations with allies and partners in the region who are most affected by China’s expansion and intensifying assertiveness is a key piece of Obama’s Asia strategy, officials say.

They add that dealing with the challenge of China’s transformation from a regional player to a global power largely through engagement and cooperation is also a hallmark of Obama’s Asia policy that will be handed off to the next administration.

From the perspective of some Asia analysts, however, Obama’s embrace of China as a great power even as he has moved to deepen ties to China’s smaller neighbors has led to confusion across the region.

Green of CSIS says a certain “back and forth” by Obama between recognizing China’s “core interests” in the region on one hand and asserting a “rules-based order” in defense of smaller nations on the other has raised doubts about the US-Asia stance.

Others say they expect the tougher side of the president’s China policy to take the spotlight when Obama meets with President Xi.

“There’s going to be a very sharp message on the concerns about maritime security [in the South China Sea] about cybersecurity, about trade and investment challenges in the relationship which are heating up as well,” says Michael Goodman, senior adviser for Asian economics at CSIS and a former director for international economics on the National Security Council. The trend in US-China relations has increasingly been “to manage competition,” he adds.

US future as a Pacific power

Just how far this framework of cooperation within competition will carry over into post-Obama US-China relations remains a question, with most analysts anticipating testier bilateral relations no matter who lands in the White House. Chinese officials are particularly wary of Hillary Clinton, regional experts say, because they see her being tougher on regional security issues and view her as the author of the US “rebalance” to Asia, which they do not favor.

But Goodman says that much of the discussion around the US future as a Pacific power will be moot if the US fails to cement an economic partnership with the region.

“TPP is absolutely essential to the pivot, the rebalance strategy, it’s essential to the US position in Asia,” he says. “It is going to be tremendously damaging to US credibility, the sense that the US is a credible partner, if we look like we’re willing to walk away from TPP.”