The South China Sea, at least until last year, was the most important strategic issue in the Asia-Pacific, and certainly in the top five of potential global hotspots.

The reasons were obvious. With China flexing its muscles in an effort to dominate one of the most important bodies of water in the world — one through which over $5.3 trillion in seaborne trade passes and underneath which untold natural resources lie buried — tensions throughout the region were skyrocketing.

In fact, after Beijing lost a major international court case to the Philippines last summer, invalidating most of its claims to the South China Sea, the stage looked like it was being set for a superpower showdown not seen since the days of the Cold War. One senior Pentagon staffer even told me last July that "if World War III is going to break out in the next decade, my bet is on the South China Sea being the place the first shot is fired."

What a difference nearly a year can make.

Thanks to a whole host of factors — China reacting calmly to the ruling, Philippine President Rodrigo Duterte trying to make nice with Beijing for economic reasons, and the transition of administrations in America — the South China Sea has dropped off the list of Washington's top foreign policy priorities.

That's a big mistake. While clearly the Trump administration's top security priority should be North Korea, America simply cannot allow China to slowly but surely dominate this important waterway. Beijing has already built seven islands out of reefs and underwater features and placed military bases and harbors on top of them. It will soon be able to permanently deploy large numbers of submarines, bombers, and fighters in the area.

But when the South China Sea has popped back on Team Trump's radar, they pulled out the same worn-out playbook the Obama administration used: relying on sailing ships around China's fake islands to dispute their claims to the waters around them. That could wind up being a major miscalculation — one that China could capitalize on.

A little background is needed to make the point.

In order to convey the idea that America would "fly, sail, and operate wherever international law allowed" in the South China Sea, the Obama administration used a strategic play called a FONOP, or freedom of navigation operation. The goal of such a mission — and I am highly simplifying here — is straightforward: Take a U.S. Navy vessel and sail it very close to an island or ocean feature to show you do not recognize certain nations' claims to a body of water.

Such actions did not work for the Obama administration, and they won't work for Trump either. While such a move does show America is trying to do something to push back on China's excessive claims and it has the benefit of good optics (something the administration very much needs these days), from a strategic standpoint they do nothing to slow Beijing's dominance of the South China Sea.

And things are only getting worse. Recent news reports have confirmed what experts like myself have always feared: China is taking its control of the South China Sea underwater. Beijing is working to build an underwater radar network to diminish the stealth capabilities of U.S. submarines and others who would operate in the area. So, as Washington simply sails around the South China Sea, Beijing presses ahead with installing ever-more advanced pieces of military hardware — above and now below the water. Beijing's new islands and equipment are permanent while America's naval excursions are just temporary, vessels destined to simply float away.

The good news is the Trump administration has options — and a prime opportunity to reverse course thanks to a timely diplomatic visit to Washington, D.C., this week by Vietnamese President Tran Dai Quang. Since Vietnam is one of the key claimants opposite China in the South China Sea, the Trump administration has been given a golden opportunity to do some bridge building. Hanoi has been looking for support from Washington on this issue for years; even if President Trump just declared the South China Sea a critical issue and asked his Vietnamese colleague to allow regular port visits by U.S. naval vessels, it would demonstrate that America is not backing down in the face of Chinese pressure.

From here, there is a lot the administration can do. The most obvious is that Team Trump needs to develop a comprehensive strategy to ensure China is not able to turn the South China Sea into its own personal lake — something the Obama administration failed to do. This could include telling Beijing in no uncertain terms that it can't take Scarborough Shoal — one of the most strategic features in the area and constantly rumored to be China's latest fake island — and turn it into Beijing's next South China Sea trophy. Additionally, if Beijing wants to push forward in changing the status quo, America could remind them it has options as well — like a big arms packages to Taiwan, something Taipei has been asking for that would surely rattle Beijing.

Clearly Washington has options when it comes to reigning in Beijing's excessive claims in the South China Sea — but sailing a boat around an island and then going home isn't one of them.