– South Korea settled disputes with the Trump administration over steel tariffs and the revision of a free-trade agreement this week. With those stumbling blocks cleared, it hoped the two governments could focus on the more pressing crisis of North Korea’s nuclear weapons.

As it turned out, South Korea was celebrating too early.

On Thursday, President Donald Trump said he might postpone finalizing the trade agreement with South Korea, which he had earlier described as “a wonderful deal with a wonderful ally,” until he secured a deal in denuclearizing North Korea.

“You know why?” he said. “Because it’s a very strong card.”

By tying a trade deal with South Korea to progress in denuclearizing North Korea, Trump is showing how little direct leverage Washington has over the isolated, nuclear-armed North just as South Korea and the United States prepare for talks with Kim Jong Un, the North’s leader.

Instead, analysts say, Trump has been left to exert leverage on South Korea, which is taking the lead in orchestrating the talks, and the South’s president, Moon Jae-in.

“Things are not going as Trump has wished for, so he is twisting South Korea’s arms so that Moon will work for the kind of results Washington wanted when he meets with Kim Jong Un,” said Koh Yu-hwan, a professor of North Korean studies at Dongguk University in Seoul, the South Korean capital. “Like the businessman he is, Trump is telling Moon, ‘I will pay you — when you produce the results.’ ”

Previous U.S. administrations used the military alliance that South Korea depends on for its security as leverage in securing U.S. interests in trade and other negotiations, but they did so in low-key negotiations, South Korean officials said. Trump has made much of that process public.

But Trump’s decision to link the trade deal with South Korea to a breakthrough in denuclearizing North Korea shows a growing unease in Washington, analysts said. Washington fears that Seoul might drift from their alliance and move closer to Beijing, while Trump feels his approach to North Korea is being undermined in the wake of a flurry of diplomatic initiatives by Kim in recent weeks, especially his meeting this week with China’s president, Xi Jinping, analysts said.

When Kim began seeking talks this year after ratcheting up regional tensions with a string of nuclear weapons and intercontinental ballistic missile tests, U.S. officials argued that he had done so because of pressure from Trump, including the threat of sanctions.

But analysts say Kim had already been planning to seek talks at the end of a hurried effort to complete what he called “a state nuclear force” last year. Analysts say his goal was to enter negotiations with Washington with a much stronger hand than his father and predecessor, Kim Jong Il, had in the 1990s and 2000s.