– President Donald Trump's national security adviser, John Bolton, fleshed out his boss' "America First" foreign policy Monday, disparaging an international organization vilified by conservatives and reaffirming a pro-Israel tilt in the Middle East. But on one of Trump's signature projects, nuclear diplomacy with North Korea, he parted company.

On the same day that the White House welcomed a letter to Trump from Kim Jong Un proposing another meeting of the two leaders, Bolton struck a markedly less optimistic tone, expressing frustration that Kim had not yet begun to fulfill his promise to rid North Korea of its nuclear weapons.

"The possibility of another meeting between the two presidents obviously exists," he said, "but President Trump can't make the North Koreans walk through the door he's holding open. They're the ones that have to take the steps to denuclearize, and that's what we're waiting for."

Bolton's remarks came after a speech to the Federalist Society in which he threatened the International Criminal Court with sanctions if it investigated U.S. troops in Afghanistan. He also announced that the United States would shut down the Palestine Liberation Organization's office in Washington, reinforcing how far the White House has moved from the role of a broker in the region.

Taken together, Bolton's unyielding remarks and the White House's upbeat analysis revealed the crosscurrents in this White House: The president's aides have translated his instincts into a range of conservative policies, but they remain skeptical of — and sometimes seek to curb — his unswerving belief that personal relationships can triumph over geopolitical realities.

Days after Trump expressed high hopes for the letter from Kim, White House press secretary Sarah Huckabee Sanders said Kim wanted to schedule a follow-up to the Singapore summit in June, and that the White House was open to it.

The military parade held in North Korea last weekend was an encouraging sign, she said, because it did not feature the usual display of intercontinental ballistic missiles that could threaten the U.S. homeland. Bolton was asked about the same parade but did not credit the North Koreans with any symbolic show of goodwill. He instead emphasized that Kim had agreed to give up his nuclear arsenal in a year.

A longtime fixture in conservative foreign policy circles, who worked in the George W. Bush administration, Bolton has kept a lower profile since he replaced Lt. Gen. H.R. McMaster than some of Trump's other foreign policy advisers.

He has been especially circumspect on North Korea since he argued, early in his tenure, that Libya could serve as a model for North Korea's disarmament. The comparison drew a furious response from North Korean officials and nearly derailed Trump's meeting with Kim.

Yet officials said Bolton has moved swiftly to assert control over other issues he cares about: Iran, the Middle East and America's role in international organizations (he had a famously rancorous stint as ambassador to the United Nations under Bush).

That was clear Monday in his virulent condemnation of the International Criminal Court. As an undersecretary of state and later ambassador, he championed Bush's decision not to join the court and led a public campaign to ­discredit it.

"Today, on the eve of Sept. 11, I want to deliver a clear and unambiguous message on behalf of the president," Bolton declared. "The United States will use any means necessary to protect our citizens and those of our allies from unjust prosecution by this illegitimate court."

"We will ban its judges and prosecutors from entering the United States," he added. "We will sanction their funds in the U.S. financial system, and we will prosecute them in the U.S. criminal system. We will do the same for any company or state that assists in an ICC investigation of Americans."

Bolton said his remarks were prompted by indications that the court wants to investigate the conduct of U.S. troops in Afghanistan. He said the goal was to stop the investigation in its tracks, and offered a litany of familiar arguments against the court: It infringed on U.S. sovereignty, had unchecked power and was "ineffective, unaccountable, and indeed, outright dangerous."

Bolton said his campaign against the court was one of his proudest moments. After he left the Bush administration in 2006, the White House showed a little less resistance to the court's work, even expressing support for its investigation of atrocities in Darfur, Sudan.

Under President Barack Obama, the U.S. began helping the court in investigations and shifted to what Harold Koh, then the State Department's legal adviser, called "positive engagement."

Still, the U.S. never joined the court. And with Bolton back in power, the White House has swung back to the language of 2002 and 2003.

"The largely unspoken, but always central, aim of its most vigorous supporters was to constrain the United States," Bolton said.

Given Bolton's history, lawyers and human rights activists said they were not surprised that the Trump administration would revert to a hostile stance. But some said they were troubled by his threats against the court's judges. "You don't win cases by threatening judges," said Stephen Rapp, former ambassador-at-large for war crimes issues under Obama. "We can prevent the prosecution of Americans, not by threatening judges, but by showing that we thoroughly investigated and found no cases where the evidence met the burden of proof."

Bolton said he did not oppose all international organizations — NATO, he said, advanced U.S. interests. But he said the Trump administration had moved systematically to withdraw from, or deny funding to, organizations like the U.N. Human Rights Council, which he said infringed on U.S. sovereignty.