YJ Fischer served at the State Department from 2012-2016. She co-wrote the 2016 Democratic Party platform and served on the Clinton-Kaine Transition Team. The views expressed in this commentary are her own.

(CNN) North Korean leader Kim Jong Un's recent threat to pull out of the upcoming summit with President Donald Trump appears to be a ploy to take advantage of Trump's main weakness as a negotiator: He often makes major concessions without securing anything of significance in exchange.

Trump has already conceded more than he should. North Korean leaders have tried for two decades to get a meeting with an America president because they believed it would give them prestige and legitimacy. Trump agreed without securing a single commitment first -- a missed opportunity.

Then, when Kim bluffed and threatened to walk away from the summit that he so desperately wants, Trump made an additional concession and, according to CNN , shifted a planned flight of B-52 bombers so as not to fly over the Korean Peninsula. (The Pentagon has declined to comment on the matter. )

Both concessions are significant and give Kim the upper hand heading into the summit.

For Trump to succeed at the summit, he has to impress upon North Korea that the US will drive a hard bargain. Instead, Trump keeps signaling to Kim that he can be taken advantage of by both adversaries and allies. Kim watched Trump do this twice this past week.

First, Trump caved to China. Trump decided he would assist the Chinese technology company ZTE, even though the company is a repeat violator of US sanctions against Iran and North Korea. Sparing ZTE punishment weakens US sanctions by signaling that Trump may not be serious about enforcement.

Moreover, ZTE is a known national security threat . FBI Director Christopher Wray told Congress that ZTE products allow China to spy on Americans, and the Pentagon has said that ZTE devices "may pose an unacceptable risk to the department's personnel, information and mission."

In exchange for offering to help ZTE, which is important to the leadership in Beijing, Trump should have insisted on receiving significant economic or security concessions from China. He could have demanded that China end its widespread practice of industrial espionage against US businesses, reduce barriers for foreign companies entering China and stop dumping artificially cheap products into the American market. Instead, he decided to go easy on ZTE, without getting anything in return.

Trump did the same with Israel. The Israelis have been pressing the United States to move the embassy for more than 20 years , in the hopes that it would signal international recognition of Jerusalem as the undivided capital of the Jewish state and a rejection of the Palestinian claim to East Jerusalem.

Trump came into office saying he would secure an Israeli-Palestinian peace deal: "I will do whatever is necessary to facilitate the agreement -- to mediate, to arbitrate, anything." Moving the embassy may have torpedoed any efforts to revive the comatose peace process.

Nonetheless, Trump should have pressed Israel for a concession in exchange for such a sought-after diplomatic coup. Trump could have insisted on the halting settlement construction, an increase in humanitarian aid to Gaza or progress on the sticking points of past negotiations, such as a realistic timeline for removing Israeli troops from the Jordan Valley. Instead he got nothing in return.

Trump's handling of ZTE and the embassy in Israel demonstrate his tendency to give away bargaining chips without getting enough in exchange.

Now, as Kim and Trump head into a June summit, North Korea has all the leverage. And Trump needs to do better at giving away less and extracting more.

This would be a difficult for any American president when it comes to North Korea because the question of how much the US should be willing to give in exchange for verifiable concessions is a truly hard one. The US wants the paranoid Hermit Kingdom to open up to international inspectors, dismantle the nuclear program it's spent years building and halt production of fissile material.

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But what meaningful concessions are we willing to provide in return? Experts have proposed economic relief and ending joint military exercises with South Korea, but those steps are unlikely to be enough.

That's why it's truly worrisome that even before sitting down with Kim and extracting an agreement to verifiably disarm his nuclear program, Trump reportedly signaled his openness to removing US troops stationed in South Korea. (The White House denies such a suggestion was made.) Such a concession, though, would be the ultimate win for North Korea as well as a victory for China, which wants US forces gone so that it can pursue its territorial ambitions in East Asia unencumbered.

Trump faces some hard questions about what to offer North Korea. He has shown this week with how he has handled China, Israel and North Korea that he is ill prepared for the tough choices ahead.