BRUSSELS — China and its increasingly sophisticated and far-flung military sit atop U.S. Defense Secretary Mark Esper’s list of international security worries, but in Europe a bigger concern is closer to home: Russia.

The Trump administration has been trying since 2018 to reorient its defense strategy toward China, with reduced focus, when possible, on Russia and the years-long insurgency wars in the greater Middle East. Russia remains a U.S. worry, but Esper and other administration officials want the allies to see China as Washington does — as a far more capable adversary.

China was not on the formal agenda when Esper met with allies at NATO headquarters Wednesday and Thursday, but he made a point of publicly expressing American concerns.

“I’ve raised it every time I’ve been here, about the ‘great power’ competition with China and Russia — but China in particular,” he told reporters.

NATO’s emphasis on Russia over China reflects the alliance’s 71-year history. Throughout that time, it has been focused mainly on Russia and the former Soviet Union. And NATO nations — especially those on Russia’s eastern flank — have grown warier of Moscow since its takeover of Crimea in 2014 and its incursion into eastern Ukraine.

More recently, Russian President Vladimir Putin has trumpeted his nation’s pioneering development of futuristic weaponry, calling into question the effectiveness of U.S. defenses and raising the possibility of a new arms race.

European allies have also been uneasy with President Donald Trump’s approach to Russia. Trump’s warm words for Putin, his resistance to accepting intelligence findings of Russian interference in U.S. elections and his desire to withdraw U.S. troops from areas, like Syria, where Moscow could fill the vacuum have caused distress within NATO. Trump’s decision to delay military aid to Ukraine last year was at the core of impeachment proceedings that ended in the president’s acquittal.

The Trump administration, meanwhile, sees Europe as slow to respond to threats posed by China. It worries that China’s economic engine is driving it to greater international influence, not just on the military front but also in global trade, in space and in technological advances. Russia, by contrast, is seen by the U.S. administration as a second-rate power, albeit with a huge nuclear force.

Trump’s national security adviser, Robert O’Brien, recently touched on this China-Russia distinction in describing the administration’s interest in nuclear arms control talks that include China as well as Russia. Trump has said his priority is an arms control deal that would include China for the first time, though China has not publicly expressed an interest in such negotiations.

“Candidly speaking, the Chinese are better prepared to have an arms race and to do what they want than the Russians ever were,” O’Brien said at the Atlantic Council this week.