Although little noticed, China is dramatically ramping up its pressure on Taiwan.

On Thursday, China unilaterally announced it is introducing four new commercial flight routes that pass extremely close to Taiwanese territory. While China says these routes are needed to reduce congestion and will be limited to civilian air traffic, Taiwan rightly suspects this is an effort to encroach on their territory. In turn, Taiwan's president used unusually strong language to condemn the Chinese action.

Cross-strait stability is impt to regional stability. Recent unilateral actions by #China – including M503 flight route & increased military exercises – are destabilizing & should be avoided. #Taiwan will continue to safeguard the status quo. We call on all parties to do the same

— 蔡英文 Tsai Ing-wen (@iingwen) January 5, 2018

Still, this is only the latest in a series of provocative moves from the Chinese government. In recent months, the Chinese military has conducted an increasing number of aggressive operations near Taiwanese territory.

The varied nature of Chinese military flights is of particular concern here. After all, rather than flying fighter jets or maritime surveillance aircraft alone, the Chinese are employing advanced surveillance aircraft purposed towards identifying a range of ground targets. Such targeting would be a necessary precursor to any Chinese invasion of Taiwan.

Equally ominous was President Xi Jinping's new year address to the Chinese military, this week, in which he told recruits they should "neither fear hardship nor death."

Yet, the most serious concern isn’t what the Chinese are doing but how Xi is thinking. Because as President Xi has consolidated his domestic position over the past year, he has embraced an overtly expansionist pursuit of Chinese influence abroad.

While much of this influence is rendered in economic terms, China’s militarization of the South and East China Seas and its refusal to exert significant pressure on North Korea indicate its desire to aggressively displace American power. In turn, with Xi believing that Taiwan's independence is a stain on the honor of the Chinese nation, newly aggressive actions against Taiwan cannot be ruled out.

So what should the U.S. do?

First, President Trump should note that the U.S. government is paying close attention to China’s increasing aggression. This is necessary not simply to ensure that China knows it is on notice, but to pare back Xi’s justified confidence that he is successfully manipulating President Trump. Fortunately, Trump has a strong record on Taiwan: earlier this year, the White House authorized a new arms sale that the Obama administration had blocked. Trump should listen carefully to any new requests from Taiwan for U.S. arms sales

Second, Trump should encourage U.S. partners in Europe, Asia, the Pacific and the Middle East to express their shared concern about what China is doing. Xi is desperate to consolidate his global position, so will pay close heed to any developments that might jeopardize his foreign relationships. Indeed, Trump's friend, French President Emmanuel Macron will make a state visit to China next week, so the timing is ripe for positive action here.

Third, Trump should upset the Chinese by sailing a carrier strike group proximate to Taiwan. Such action would reassure Taiwan, deter China and also offer the U.S. Navy a valuable exercise in near-China operations. And by conducting this deployment while avoiding a transit of the Taiwan Strait, the U.S. would avoid over-escalating against China while also dangling more aggressive moves in the future.

Ultimately, however, the U.S. must not sit idle here. The Chinese are very obviously testing the waters.