David A. Andelman, a CNN contributor and columnist for USA Today, is the author of "A Shattered Peace: Versailles 1919 and the Price We Pay Today." He formerly served as a foreign correspondent for The New York Times and Paris correspondent for CBS News. Follow him on Twitter @DavidAndelman . The views expressed in this commentary are his.

(CNN) There was a frightening new guest at the party that marked Russia's Navy Day celebrations this past weekend -- perhaps representing the greatest single global challenge for President Donald Trump.

All were fresh from the first stage of Joint Sea 2017 , a Russian-Chinese naval exercise that Chinese media boasted included live-firing of big guns in the Baltic Sea, which borders five of America's NATO allies, and was designed at least in part to showcase the cream of both nations' seaborne military might.

At the same time, China was staging its own military parade in Beijing as President Xi Jinping watched while dressed in the green camouflage uniform of the People's Liberation Army. Some 12,000 officers and men, accompanied by tanks, long-range missile launchers, jet fighters and other new, modern weaponry, moved past.

All this display of military muscle was just the latest and most visible -- though perhaps least appreciated -- headache for Trump in world trouble spots, from Syria to North Korea

China pivoting to Russia at this moment in time cannot be a good thing on any number of levels. The sudden alliance of these nations in the face of pressure from Trump suggests that those headaches are not going get any easier to solve anytime soon.

These joint efforts -- coinciding with the United States, Japan and South Korea staging their own maneuvers close to both China and North Korea -- suggest that both China and Russia had arrived at a newfound independence in the face of American challenges.

Moreover, their allies in Syria and North Korea will now realize they have two potent counterweights to their efforts to chart their own potentially deadly courses.

North Korea has relied for decades on the assistance of China, particularly on an economic level, to prop up its failing and utterly despotic regime while counting as well on the neutrality of Russia, with which it shares a sliver of its northern frontier.

Indeed, North Korean territory is barely 100 miles from the main Siberian port of Vladivostok, where Russia happened to stage the eastern tranche of its Naval Day exercises last weekend.

JUST WATCHED Russia shows military might during Navy Day Replay More Videos ... MUST WATCH Russia shows military might during Navy Day 00:10

At the same time, additional Naval Day exercises were taking place at the huge Russian air and naval base at Tartus in Syria on the eastern Mediterranean, which Russian media reported included six warships.

This will have only given comfort to Syrian President Bashar al-Assad, whose regime is being propped up by Russian air and naval power, much of it based in Tartus.

One of Putin's principal reasons for backing Assad's alleged attacks on the rebellion that has challenged him is to maintain this single toehold in the Mediterranean -- central to the strategic position of NATO and America in Europe and the Middle East.

China and Russia for years have propped up diplomatically and economically both North Korea and Syria -- often exercising their vetoes in the UN Security Council to beat back Western challenges to their allies' more outrageous actions.

That the two powers are joining forces can only give comfort to North Korea and Syria, knowing that it will now be even harder for the United States to influence their actions.

This new reality should not have come as a surprise.

JUST WATCHED US detects odd sub activity from North Korea Replay More Videos ... MUST WATCH US detects odd sub activity from North Korea 01:29

On June 7, Chinese Defense Minister Chang Wanquan met his Russian counterpart, Sergey Shoigu, during a summit in Kazakhstan of the Shanghai Cooperation Organization, a 20-year-old military and political grouping of China, Russia and other former Soviet Asian republics.

Shoigu proposed signing a comprehensive military cooperation agreement between Russia and China.

And sure enough, three weeks later, Xi stopped by Moscow en route to the G20 summit in Germany, where he confirmed that such an agreement had been signed, along with $10 billion worth of other agreements, as both leaders grinned and shook hands.

So, with Russia now firmly in its corner, and the 2,615-mile frontier the two nations share thoroughly secure, how much further will China go in defying Trump? How long might Beijing stay quiet on further pressures against Kim Jong Un's headlong dash toward a nuclear arsenal and intercontinental ballistic missiles?

At present, North Korea poses no real threat to China. And it won't until its present government collapses and large numbers of North Koreans pour across the 880-mile border that the two nations share, or nuclear war breaks out, threatening to rain destruction on the millions of Chinese clustered in major cities within a 100-mile nuclear blast radius around Pyongyang, the North Korean capital.

Both of these unlikely scenarios will have at least slightly restrained China's actions in the past. But now, with a military ally in Russia, its independence may know even fewer bounds.

This must be taken into consideration before Trump or Congress considers how the United States tightens the screws on China -- or Russia for that matter.

After the latest expulsions and sanctions engineered by Washington and Moscow, it's hardly likely that Trump will be able to use any goodwill from Putin to influence Chinese rhetoric or activities over North Korea.

Now, Trump must reflect carefully how truly potent a combined Sino-Russian alliance may be as a counter to any moves he might consider going forward.