Jennifer M. Harris is a senior fellow at the Council on Foreign Relations and co-author of " War by Other Means: Geoeconomics and Statecraft ." The views expressed are her own.

(CNN) Major geopolitical crises have a way of greeting US presidents soon after taking office. Nazi Germany's withdrawal from the League of Nations in 1933, the Soviet-led construction of the Berlin Wall in 1961, the Gulf of Tonkin incident in 1964 -- all were among the most daunting tests of US foreign policy in the past century, and all came less than a year into the tenures of new US administrations.

This is no accident. Foreign governments often like to test a new White House early on. Indeed, Russia appears to have already commenced its testing of Trump's Washington; a resurgence of heavy fighting in Eastern Ukraine suggests Moscow may be embarking on an offensive that could redraw Ukrainian borders beyond Crimea.

If past is precedent, Beijing will also soon look to stress-test the new White House. How President Trump responds could well determine whether he stays in the driver's seat of his own legacy.

Already, there are concerning signs of conflict to come, and the Trump administration's early missteps on the South China Sea conflict could give Beijing the pretext to manufacture a crisis. Should he take the bait, President Trump risks allowing external foreign policy crises to define his tenure, not unlike the way 9/11 reshaped George W. Bush's presidency.

The trouble began when Secretary of State Rex Tillerson suggested during his confirmation hearing that the United States would block China from accessing islands it has built in the South China Sea, islands Beijing has outfitted with weapons systems and military-grade airstrips.

While much of Washington sprung into damage-control mode -- most China experts dismissed Tillerson's remarks as a misstatement -- the White House doubled down on Tillerson's comments, raising the possibility that a US blockade of China in the South China Sea means just that.

Beijing so far has shown marked restraint, at least in its official statements. The Chinese Foreign Ministry downplayed Tillerson's initial comments and refused to speculate on how it would react to a "hypothetical" situation. Its message for domestic audiences, though, was less conciliatory.

"Unless Washington plans to wage a large-scale war in the South China Sea," the nationalist-leaning Global Times warned , "any other approaches to prevent Chinese access to the islands will be foolish."

For a country whose largest challenge is arguably in managing the expectations of its own people, such hawkish messages may be the more reliable sign.

Such escalations are likely to come in two varieties. Most obviously, Beijing could respond militarily. China could declare an "air defense identification zone," or ADIZ, in the South China Sea, just as it did in the East China Sea in November 2013 . This would effectively mean Beijing drawing lines in the air to mirror its claims in the South China Sea waters below.

More worryingly, China could begin building out more of the military infrastructure it has already installed in certain pockets of the South China Sea. China has already militarized one of its artificial islands (near the Spratly Islands chain), equipping it with weapons systems and military-grade landing strips. If they were to do likewise near the Scarborough Shoal -- within striking distance of the Philippines and US military bases -- this would almost certainly cross a red line for the United States.

A composite image of Gaven reef taken on November 17.

But while Washington tends to focus on military scenarios, China is just as skilled at using economic instruments to advance its maritime claims. Unlike the legions of Pentagon strategists poring over military scenarios, much of China's economic coercion goes unnoticed and unanswered by Washington.

It has already proven effective.

For example, the Philippines won a three-year UN arbitration case against China this past July. Yet by the time the ruling was issued, Philippine President Rodrigo Duterte had already undermined much of its force. Duterte repeatedly hinted at possible concessions in exchange for economic cooperation with Beijing, even going so far as to offer to "shut up" about the dispute in return for investment.

Any escalation between Washington and Beijing, coming just as Russia seems to be mounting a major offensive in eastern Ukraine, would stretch the Trump foreign policy team well beyond its depth. So what can the administration do to head off a crisis? Three broad actions are urgently needed.

First, US military leaders must provide much-needed clarity, signaling precisely what countermeasures China can expect should Chinese officials opt to declare an ADIZ in the South China Sea, militarize near the Scarborough Shoal, or otherwise escalate militarily.

Follow CNN Opinion Join us on Twitter and Facebook

Second, US congressional leaders must pass new legislation (known as AUMF) more clearly delineating the President's unilateral discretion concerning the use of US military force -- and reasserting Congress' role in green-lighting US military combat, especially in cases (such as this) involving risk of conflict between major powers.

Third, Congress and the White House together must work to equip US policymakers with the option of reaching for something other than military might. The rising military contest in Asia is real, but focusing too narrowly on it risks obscuring the larger struggle for leadership in the region, which remains primarily economic. If Washington is to curb Beijing's expansionism, it will need to make China bear the economic costs of its growing bellicosity. It will also need to steel its Asian allies, countries such as Japan and the Philippines, against Chinese economic bullying.

These things must happen before Washington gives in to any military escalation in Asia.

China's greatest military strategist, Sun Tzu, once said, "If you know the enemy and know yourself, you need not fear the result of a hundred battles." President Trump would do well to heed this advice, because right now he doesn't appear to know either.