WASHINGTON — With the United States preoccupied by the sobering reality of more than 100,000 Americans dead from the coronavirus, China has pushed in recent weeks to move troops into disputed territory with India, continue aggressive actions in the South China Sea and rewrite the rules of how it will control Hong Kong.

At roughly the same time, Russian fighter jets roared dangerously close to US Navy planes over the Mediterranean Sea, while the country’s space forces conducted an anti-satellite missile test clearly aimed at sending the message that Moscow could blind US spy satellites and take down GPS and other communications systems.

Iran, Secretary of State Mike Pompeo said, is reestablishing the infrastructure needed to make a bomb — all a reaction, the Iranians insist, to President Donald Trump’s decision two years ago to reimpose sanctions, reaffirmed in recent weeks as the State Department dismantled the last elements of the Obama-era nuclear deal.

The coronavirus may have changed almost everything, but it did not change this: Global challenges to the United States spin ahead, with America’s adversaries testing the limits and seeing what gains they can make with minimal pushback.

And with the United States looking inward, preoccupied by the fear of more viral waves, unemployment soaring over 20 percent and nationwide protests ignited by deadly police brutality, its competitors are moving to fill the vacuum, and quickly.

In some cases, Trump has helped them along. His announcement Friday that the United States was severing ties with the World Health Organization left the field clear for China to broaden its influence over the organization. On Saturday, Trump delivered a gift to President Vladimir Putin of Russia: He said he would invite Putin to an expanded meeting of the Group of 7 nations. Russia was banned after its 2014 annexation of Crimea and attacks on eastern Ukraine.

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“The scope of medical and economic disruption that will come from COVID-19 will leave opportunities for both nations, and others, to try to gain advantages,” Stanley A. McChrystal, a retired four-star commander of the Joint Special Operations Command and American forces in Afghanistan, said.

The United States has not stayed entirely on the sidelines, though. The race for a coronavirus vaccine has come to involve both China’s People’s Liberation Army and the US military, which has said it would mobilize to distribute any breakthrough discovery.

US warships have sailed into disputed waters in the South China Sea in recent weeks to assert freedom-of-navigation rights, continuing a standoff in a region that Beijing asserts is its territory.

And the United States is speeding ahead in a renewed conventional and nuclear arms race, though its strategic rationale — other than to overmatch Russia and China — has never been fully described by this administration.

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MIDDLE EAST POWER VACUUM

It is not only China and Russia that are challenging the United States. Across the Middle East, there is a sense that Trump’s oft-expressed desire to withdraw from the region offers new leeway.

Iran has bet that Trump is not willing to risk outright confrontation. Tehran has gradually accelerated its production of nuclear fuel and ignored requests from international inspectors for access to suspected nuclear-related sites.

And in the Persian Gulf, Tehran is episodically testing America’s limits.

Nearly a dozen Iranian fast boats conducted what the Navy described as “dangerous and harassing approaches” to 6 US warships in the Persian Gulf in mid-April, prompting Trump’s order “to shoot down and destroy any and all Iranian gunboats if they harass our ships at sea.” Iran backed off in the Gulf — but then stepped up oil shipments to Venezuela, in a challenge to the US-led embargo meant to displace President Nicolás Maduro.

In mid-May, Iran’s foreign minister, Mohammad Javad Zarif, said US attempts to disrupt the course of Iranian tankers carrying fuel for Venezuela were “dangerous” and “provocative” acts.

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Russia and China are active in the region. Russia continues to support the government of President Bashar Assad as he nears a brutal victory in Syria’s civil war. And China maintains a military base in Djibouti, near a US one there.

“China has significantly expanded its engagement in the region, especially in the economic and diplomatic realms,” said Patricia M. Kim, a China analyst at the US Institute of Peace who worked on a recent report on China and the Red Sea area. “And for the US to remain relevant — to be able to shape norms in the region and help states manage China’s growing presence — it needs to significantly increase its own engagement.”

FROM RUSSIA, TESTING BOUNDARIES

Trump’s willingness to invite Putin back into the company of the major Western allies is all the more mystifying because friction between American and Russian forces is running high.

On Friday, 2 US Air Force B-1B bombers flying a long-range training mission over the Black Sea prompted Russian fighter jets to scramble and intercept the US warplanes. At least 3 times in the past 2 months, Russian fighter jets intercepted Navy P-8 surveillance planes over the Mediterranean.

But Trump has not been eager to ratchet up tensions with Russia. “I don’t see it,” Trump said when asked whether Russia was toying with US military forces. “We had a very good relationship with Russia.”

That is not what top NATO officials and American commanders say.

The US military Tuesday accused the Kremlin of secretly sending at least 14 fighter jets to eastern Libya in May to support Russian mercenaries battling alongside a beleaguered commander, Khalid Hifter, in his campaign to oust the internationally recognized government.

The criticism by 2 top American generals underscored the Pentagon’s broader concern about Moscow’s growing influence in Libya and a looming security threat on NATO’s southern flank.

In mid-March, 2 Russian strategic bombers flew over a US submarine that surfaced in the Arctic Ocean and were subsequently escorted by American and Canadian fighter jets.

“What we do see is, I think, a continuous effort for them — as they do in the COVID-19 environment, outside the COVID-19 environment — to continually probe and check and see our responses,” said Gen. Terrence J. O’Shaughnessy, head of the military’s Northern Command, which oversees homeland defense.

CHINA SEIZES THE MOMENT

During the 2016 campaign, Trump spoke publicly about leaving it to South Korea and Japan to secure the Pacific. And as Trump has argued with Seoul and Tokyo, President Xi Jinping of China has seen his moment of opportunity.

“I think what Beijing is pursuing — and it’s a rational interest — is hegemonic authority over Asia,” said Elbridge Colby, the former Pentagon official who was the main writer of the Trump administration’s National Defense Strategy, which focuses on how the US military should reshape itself for great-power competition with Russia and particularly China.

It is most evident in the South China Sea. Turning outcroppings of rock into full islands, it is forming a bulwark against the claims of competing nations and against the findings of a 2016 international tribunal, which sought to limit China’s aggressive maritime actions.

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In April, a Chinese Coast Guard vessel collided with a Vietnamese fishing boat near a disputed archipelago, sinking the small vessel. The same month a Chinese seismic survey ship, escorted by Chinese Coast Guard vessels, entered waters designated as the exclusive economic zone of Malaysia, daring the Malaysians to push back.

The Trump administration has continued President Barack Obama’s policy of not taking sides in the territorial disputes while asserting that the United States aims to maintain freedom of navigation in the region. Defense Secretary Mark Esper insists the United States will continue naval operations “to send a clear message to Beijing that we will continue to protect freedom of navigation and commerce for all nations, large and small.”

But China’s leaders appear to suspect that they are empty words.

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