Once upon a time, Trump mused about how well he and Russian President Vladimir Putin would get along. Then-candidate Trump said Putin had declared him a "genius," criticized the Obama administration's tensions with Moscow and said it would be better "if we got along."

China, on the other hand, was a currency manipulator, a thief of US jobs that should no longer be allowed to "rape our country." If elected, Trump promised to impose heavy tariffs on Beijing and take it to court for shady trade practices.

It turns out that wielding power -- as opposed to criticizing it -- can change your outlook.

This month, during which his administration has stepped up US military action in Syria and Afghanistan as he looks to reassert US power, Trump said that "we're not getting along with Russia at all, we may be at an all-time low." He and Chinese President Xi Jinping, on the other hand, have "a very good chemistry," Trump declared.

The President's reversal on Russia and China is part of a series of policy flip-flops that have seen Trump abandon campaign positions on NATO, Israel, the Iran nuclear agreement and US alliances in Asia.

The shifts, which bring Trump's White House in line with many Obama and George W. Bush administration policies, may not last under this mercurial president, but they reflect some hard facts about America's interests.

"Whatever the aspirations on the campaign trail, they have given way to the realities of what it takes to conduct American foreign policy in a cruel and unforgiving world," said Aaron David Miller, vice president at the Woodrow Wilson International Center for Scholars.

"The way this administration does business is highly unorthodox in so many respects," Miller said, "but the ultimate outcome on so many issues seems now to come around to a pretty conventional approach."

And so it is -- these days -- with Russia and China.

Trump had been eager to improve relations with Moscow and often expressed confidence that his ability to bond with Putin would ease friction between Washington and Moscow over Russia's role in Syria and its annexation of Crimea from Ukraine.

But Syrian President Bashar al-Assad's alleged April 4 chemical weapons attack on his own civilians triggered Trump's outrage, leading him to strike a Syrian airfield with Tomahawk missiles and seeming to mark a change in Trump's outlook on Russia -- which has supported Assad throughout Syria's bloody civil war.

JUST WATCHED Watch: CNN sent to secretive North Korea event Replay More Videos ... MUST WATCH Watch: CNN sent to secretive North Korea event 01:33

Trump's administration, shadowed by Russia's alleged interference in the US election, had already been shifting its views on Moscow as the former real estate mogul brought more figures into the White House who backed traditional foreign policy positions.

Defense Secretary James Mattis and Secretary of State Rex Tillerson, who had his own foreign policy research and risk analysis staff as CEO of ExxonMobil, along with UN Ambassador Nikki Haley, all sounded a tougher note on Russia than the President did, pointing out the ways that Moscow works to counter US interests around the world.

"They were all sounding much tougher on Russia, much more like the Obama administration, and the outlier was the White House," said Angela Stent, director of the Center for Eurasian, Russian and East European Studies at Georgetown University.

The US missile strike was an exclamation mark establishing that Trump, for the time being at least, has come to see Russia in more conventional US foreign policy terms. "You have a much more consolidated policy toward Russia now," Stent said.

Putin told Russian TV in an interview Wednesday that under Trump, the relationship between Washington and Moscow had "worsened."

Even as he took a harsher tone on the longtime US adversary, Trump still seemed to offer some reassurance in a Wednesday appearance with NATO Secretary General Jens Stoltenberg, saying that, "It would be wonderful ... if NATO and our country could get along with Russia." On Thursday, Trump tweeted that, "things will work out fine between the U.S.A. and Russia. At the right time everyone will come to their senses & there will be lasting peace!"

JUST WATCHED US strike group heads toward North Korea Replay More Videos ... MUST WATCH US strike group heads toward North Korea 02:27

But Stent said that actually there is likely to be continued US-Russia tension. "All the problems the previous administration had still remain," she said.

"You had these role reversals," according to Miller, a former State Department official, "with China as a bad guy and Putin being courted. But in the face of realities, there's been a switch. Russia basically now occupies the role that China was supposed to occupy in the Trump administration."

The "realities" that Trump faces include North Korean leader Kim Jong Un's accelerating pursuit of nuclear and missile technology. Trump sent tweets this week praising Xi for committing to help restrain North Korea, which may be on the verge of a sixth nuclear test. Beijing is Pyongyang's closest ally.

On Tuesday, Trump tweeted that he'd told Xi a trade deal with the US would be "far better for them if they solve the North Korea problem." On Wednesday, Trump tweeted that he and Xi had had "a very good call" about Pyongyang. And Thursday, the president tweeted that he had "great confidence that China will properly deal with North Korea. If they are unable to do so, the U.S., with its allies, will! U.S.A."

Sandy Pho, a senior program associate for the Kissinger Institute on China at the Wilson Center, said that Trump, like many new presidents, has been facing a learning curve on the ways of Beijing.

JUST WATCHED Watch Trump's stunning U-turns on key issues Replay More Videos ... MUST WATCH Watch Trump's stunning U-turns on key issues 00:57

"You cannot not talk to China. I think that's what he realized. It's too important," said Pho, but she warned Trump may be underestimating China's influence over North Korea and its interest in an outcome the US would be happy with.

What Beijing wants in North Korea is stability, not potentially disruptive change. "The last thing they want is a flood of North Korean refugees coming over their border," Pho said.

And the only thing Beijing might think was worse, she said, would be a unified and US-allied Korean Peninsula on the border.

If Trump thinks his new posture towards the geopolitical rivals will help him play them off against each other, Stent suggested he think again.

"I think he fundamentally doesn't understand the nature of the Russia-China relationship," she said, describing it as pragmatic. The two authoritarian governments support each other on major foreign policy problems, dislike domestic protest and see the US in a similar way.

"Both agree that we need a new world order that takes their interests into account more than it does right now, and both agree it's time to move away from a US-dominated global order," Stent said.