WASHINGTON (Reuters) - Despite his campaign vows to take a tougher line with North Korea, President Donald Trump’s restrained public reaction to Pyongyang’s first ballistic missile launch on his watch underscores that he has few good options to curb its missile and nuclear programs.

U.S. President Donald Trump listens to a translation during a joint news conference with Japanese Prime Minister Shinzo Abe at the White House in Washington, U.S., February 10, 2017. REUTERS/Joshua Roberts

The responses under consideration - which range from additional sanctions to U.S. shows of force to beefed-up missile defense, according to one administration official - do not seem to differ significantly so far from the North Korea playbook followed by Trump’s predecessor, Barack Obama.

Even the idea of stepping up pressure on China to rein in a defiant North Korea has been tried - to little avail - by successive administrations. But Beijing is showing no signs of softening its resistance under a new U.S. president who has bashed them on trade, currency and the contested South China Sea.

More dramatic responses to North Korea’s missile tests would be direct military action or negotiations. But neither appears to be on the table - the first because it would risk regional war, the latter because it would be seen as rewarding Pyongyang for bad behavior. And neither would offer certain success.

“Trump’s options are limited,” said Bonnie Glaser, an Asia expert at the Center for Strategic and International Studies think tank in Washington.

Trump’s initial public comments on Saturday on the test launch of what was believed to be an intermediate-range Musudan-class missile were unexpectedly measured - and brief - compared to earlier bluster about another U.S. adversary, Iran, since he took office on January 20.

“I just want everybody to understand, and fully know, that the United States of America is behind Japan, our great ally, 100 percent,” Trump told reporters in Palm Beach, Florida, speaking in a solemn tone alongside visiting Japanese Prime Minister Shinzo Abe.

The U.S. president did not mention North Korea or signal any retaliatory plans for what was widely seen as an early effort to test the new administration.

By contrast, Trump tweeted “It won’t happen!” in January after North Korean leader Kim Jong Un said the North was close to testing an intercontinental ballistic missile.

White House adviser Stephen Miller insisted on ABC’s “This Week” that Trump’s one-sentence statement was an “important show of solidarity” with Japan. He told “Fox News Sunday” the administration was going to bolster its allies in the region against the “increasing hostility” of North Korea.

While no one can rule out that Trump might still take to Twitter with harsh rhetoric as he often does, some analysts said his relatively subdued initial statement could show that aides have convinced him not to be baited by Pyongyang into issuing threats that would be hard to carry out, especially while his North Korea strategy is still being formulated.

VOWING MORE ASSERTIVE APPROACH

Trump’s aides have said that they will take a more assertive approach than the Obama policy dubbed “strategic patience,” which involved gradually scaling up sanctions and diplomatic pressure and essentially waiting out the North Korean leadership. But the new administration has been vague about how it would do this.

The Trump administration had been expecting a North Korean “provocation” and will consider a full range of options in response, but they would be calibrated to show U.S. resolve while avoiding escalation, the U.S. official said, speaking on condition of anonymity.

The stakes would be higher, however, if nuclear-capable North Korea makes good on its threat to test an ICBM of a kind that could someday hit the United States, analysts said.

Trump and his aides are likely to weigh new U.S. sanctions to tighten financial controls, an increase in naval and air assets and joint military exercises in and around the Korean peninsula and accelerated installation of new missile defense systems in South Korea, the official said.

Trump has also made clear that he believes China has not done enough to use its influence to help rein in Pyongyang’s nuclear and ballistic programs.

The U.S. official told Reuters that Trump would now step up pressure on Beijing, but acknowledged that there were limits to how far China would go, especially in enforcing sanctions, because of its own interests in avoiding destabilization of North Korea.

It remains to be seen, however, whether the new administration might go a step beyond Obama’s approach and focus on imposing “secondary sanctions” on firms and entities that help North Korea’s weapons programs, many of which are in China.

Also unclear is whether Trump’s phone call last week with Chinese President Xi Jinping, in which the U.S. president backed away from his threat to break from America’s long-standing “one China” policy, would engender greater cooperation from Beijing on North Korea.

“Beijing has enormous leverage over Pyongyang thanks to being one of its only trading partners and in fact could not survive without Chinese economic assistance,” said Harry Kazianis, director of defense studies at the conservative Center for the National Interest.

Riki Ellison, who heads the Missile Defense Advocacy Alliance, an industry group, said Trump should also move quickly to beef up missile defense in both South Korea and Japan - for which the Obama administration has already laid much of the groundwork. “He cannot ignore this,” he said. “It has to be swift.”

North Korea’s repeated missile launches prompted Washington and Seoul to agree to deploy a Terminal High Altitude Area Defense (THAAD) anti-missile battery in South Korea later this year, a system strongly opposed by Beijing, which worries that its powerful radar undermines its own security.