President-elect Donald Trump has not minced words on the South China Sea.

In the past few months, he's called-out Beijing in tweets and speeches for its "brazen" island-building activities and the construction of a "massive military complex."

He's also vowed to use Washington's economic leverage over Beijing as a way to push back -- a tactic that, if it's used, would open a brand new front in US-China competition, setting the scene for a possible Chinese economic retaliation in kind.

Trump's pick for secretary of state Rex Tillerson, unexpectedly, has gone even further. During his Senate confirmation hearings this week, the former Exxon Mobil chief boldly declared that China's militarization of artificial islets in the South China Sea was "akin to Russia's taking Crimea" from Ukraine -- a comparison that will ruffle feathers in Beijing.

Echoing the views of many Asia analysts in Trump's team and across the political spectrum in Washington, Tillerson criticized President Barack Obama's South China Sea policy for being inadequate -- implying that periodic naval patrols were not a sufficiently muscular response to stop China from continually "pushing the envelope."

But his most controversial remarks concerned what America's South China Sea goals should be going forward. Beyond convincing Beijing to stop its island-building -- which the Obama administration has tried but been unable to do -- Tillerson said: "We're going to have to send China a clear signal that first, the island-building stops, and second, your access to those islands also not going to be allowed."

No one in Washington has seriously entertained this option. Blocking Chinese naval vessels from accessing South China Sea reefs would almost certainly trigger a US-China clash. More to the point: as many of the reefs are effectively a part of international waters, preventing Chinese ships from sailing to or near them would undermine the very freedom of navigation rules that the US has been trying to uphold.

While we shouldn't read too much into this aspect of Tillerson's remarks -- after all, people make mistakes during hours-long grillings by Senate committees, especially when they're new to the issues -- the overall tone of his testimony was tough on China.

If Obama's team was at times too cautious in taking China to task, Tillerson's blunt talk of China's "extremely worrisome" and "illegal" actions will bring a sharpness to State Department policy that hasn't previously been present.

Counterproductive on North Korea?

Trump and Tillerson have also harshly criticized Beijing for its failure to help the US enforce United Nations sanctions on North Korea -- a hawkish approach that may ultimately backfire.

Although the President-elect began by tweeting about his disappointment earlier this month, Tillerson, in his hearing, turned up the heat. In unusually frank terms, he stated Washington can no longer accept Beijing's "empty promises" on North Korea and should consider putting "secondary sanctions" on Chinese entities that are violating sanctions in order to "compel" Beijing to finally comply.

They are correct Beijing should do more to enforce UN Security Council sanctions that seek to place pressure on Kim Jong Un's regime for its nuclear and ballistic missile tests. Despite agreeing to two rounds of ostensibly tough sanctions in 2016, China has consistently found ways to avoid truly enforcing these measures -- such as not sufficiently cracking down on the vast number of small Chinese companies that import North Korean coal in excess of the UN's restrictions.

But publicly deriding China for its failure to fully comply with sanctions only pushes Beijing onto the defensive. Chinese officials have already rejected Trump's accusations and talked up their own efforts to build stability on the Korean Peninsula, and will rile at Tillerson's latest rebuke. The net effect will be an acrimonious bilateral context in which US-China coordination on North Korea, or quiet pressure on Beijing, will be more difficult.As any long-term solution to restraining North Korea's nuclear ambitions will require the active participation of China, creating a public rift on this issue is counterproductive. Trump's foreign policy team should instead continue to place behind-the-scenes pressure on China over poor sanctions enforcement, using private diplomatic avenues that won't cause Beijing to clam up on cooperation.

A more unstable US-China relationship

While there is a need for firmer American action in the South China Sea and on North Korea, the Trump administration is shaping up to have a hardline China policy across the board.

Since winning the election, Trump has continued to announce that China is stealing US jobs, manipulating its currency, and regularly hacking US institutions. He and his team have stoked uncertainty over the future of US-Taiwan relations -- a core concern for Beijing -- and talked up a larger US military footprint in the Asia-Pacific, all while criticizing Chinese inaction on North Korea and its maritime assertiveness in Asian waters.

This is a mistake. Getting tough on China on everything at once isn't going to induce Beijing to cooperate or make difficult concessions.

A purely muscular approach, if this comes to pass, will make Beijing a more truculent partner for Washington across the board. The consequences will be negative for US-China relations globally -- making it harder for the two powers to work together on issues of mutual interest, such as crisis management and environmental protection, while deepening friction in major areas of disagreement, like Asia's future strategic order.

Instead, Tillerson and the rest of Trump's foreign policy team should prioritize areas where a tougher approach to China is warranted -- such as in the South China Sea -- and concentrate their efforts to affect changes there. This will, at times, require strong public statements and US actions, but should be coupled with private diplomatic pressure that's not tweeted in 140 characters or less.

Less important challenges in US-China relations will have to be sidelined for the short term or managed quietly and slowly. No major power relationship can endure hostility on all fronts at once without slipping into a Cold War-esque state.

At this very early point in Trump's incoming presidency, it seems unlikely his administration will choose heed these calls for moderation. But the reality of negotiating compromises and deals with a major power competitor may well force Trump's team to pick their battles carefully in order to get things done.

Originally published on CNN.