While the U.S. media and political establishment were focused on Russia’s hacks of the recent U.S. presidential election—and the retaliatory sanctions the outgoing Obama administration announced on Dec. 29—the Chinese navy was moving aggressively into the contested waters of the strategic South China Sea.

In a move that combined actions and words, China’s sailed its aircraft carrier boldly through disputed waters while prominent Chinese figures voiced rhetoric significantly escalating Beijing’s global ambitions.

It will mostly fall on president-elect Donald Trump and his administration to formulate a response.

It’s customary for Beijing to tease an incoming U.S. presidential administration with some kind of military or diplomatic demonstration. American experts expected the Trump administration to face some kind of challenge. And indeed on Dec. 15, the crew of a Chinese navy ship briefly hijacked a U.S. Navy underwater research drone, drawing a flurry of indignant and contradictory tweets from Trump.

But the far greater challenge came 10 days later—and could represent a sneak peak of China’s forceful approach to the United States’ military and diplomatic posture for at least the next four years.

The first obvious sign of China’s big move came on Christmas Day, when Japanese forces detected Liaoning, the Chinese navy’s first and so far only aircraft carrier, sailing out of the East China Sea into the Western Pacific for the first time.

China is currently building a second carrier, and has said it will eventually begin construction on a third flattop. The U.S. Navy possesses 10 large carriers plus nine carrier-like assault ships that can carry a modest number fixed-wing planes.

Liaoning, a former Soviet vessel that China acquired and rebuilt at great expense starting in 1998, entered Chinese navy service in 2012. Normally based at Dalían in northern China, Liaoning has spent the past four years periodically venturing into coastal waters for training. The Christmas Day sortie qualifies as the 1,000-foot vessel’s first frontline deployment.

With fighter jets and helicopters arrayed on her deck and accompanied by five heavily-armed escort vessels, Liaoning cut an arc through the Pacific just 60 miles off the coast of Japan’s Okinawa prefecture before heading southwest.

The Obama administration reacted with a practiced shrug. U.S. State Department spokesman Mark Toner pointed out that all countries have the right the sail their warships in international waters. “It’s freedom of navigation,” Toner said.

Taiwan was less sanguine as the Chinese flattop closed to within 90 miles of the island country on her way back toward China. The defense ministry in Taipei announced it “will pay close attention to [Liaoning’s] future movement.”

Tensions between the United States, Taiwan and China lately have been running higher than usual. On Dec. 2, Trump shattered decades of protocol—and drew protest from Beijing—when he spoke on the phone with Taiwanese president Tsai Ing-wen.

Since 1979, the U.S. government has carefully avoided officially recognizing Taiwan as a fully independent country—in order to avoid inciting the wrath of China, which considers Taiwan a breakaway province and has threatened to invade if the island ever makes official its own independence.

It’s possible to read Liaoning’s passage near Taiwan as a forceful retort to the Dec. 2 phone call. Even then, Beijing wasn’t done.

Sailing into the resource-rich South China Sea—where China, The Philippines, Taiwan, Vietnam, Indonesia, Malaysia and Brunei have all asserted overlapping, and unresolved, territorial claims—Liaoning hailed at Hainan, an island province of China in the South China Sea southwest of Taiwan.

Starting in 2012, China massively expanded Hainan’s port facilities to accommodate not just one full-size carrier but two. By contrast, the United States keeps just one large carrier and one assault ship in the Western Pacific. Both vessels are homeported in Japan.

Liaoning briefly stopped at Sanya on Hainan in 2013, at a time when tensions in the South China Sea were arguably much lower. The flattop’s visit three years later served as a clear reminder to nearby countries and the United States that, before too long, China will be able to quickly deploy naval power in the South China Sea that roughly matches America’s own naval contingent in the region.

And in a sharp break from the past, a Chinese official matched his country’s swelling military might with new, bombastic rhetoric. The South China Sea is China’s “ancestral sea” and also “China’s territorial waters,” Xing Jincheng, a Chinese-military political commissar on Hainan, wrote in a Dec. 29 op-ed.

Xing, who was appointed in 2013 to oversee Hainan’s naval militia, wrote that he considered it his job to wage “the first battle for the rights to the South China Sea.”

That kind of rhetoric is becoming more prominent among Chinese officials and government proxies. In a Nov. 12 speech, Dr. Zhu Feng, the director of the prestigious China Center for Collaborative Studies of the South China Sea at Nanjing University, spoke forcefully about China’s rise as a “global” military power.

In recent years, Chinese leaders have shied away from describing Beijing’s ambitions as global, instead insisting that the country merely wants to be a “regional” power—in other words, a force incapable of challenging America’s worldwide military dominance.

“To become a successful country, one must be a global power, and the global powers must be the world’s military powers,” Zhu said.

Describing the Hainan carrier base as “China’s most important naval port,” Zhu predicted that the sea route from Hainan into the South China Sea would become “the world’s most important channel.”

Just one force stands in the way of China’s “free access” to the South China Sea, Zhu stated. “For China to become a maritime power, we must limit the United States’ global naval freedom of intervention.”

“I tell you very frankly that the South China Sea dispute has just begun,” Zhu added.