The never-ending saga of US-China trade talks trudged on this week, again dominated by one theme: uncertainty.

Few details have been revealed of the agreement that both sides say is in works, while the vague contours that have emerged raise a number of concerns.

According to Washington’s envoy in Beijing, Terry Branstad, the chief sticking point is now the enforcement of any deal. Lack of clarity on this issue will also likely mean more negotiations are needed before Presidents Donald Trump and Xi Jinping meet to consummate any treaty.

“A date hasn’t been finalized,” Branstad said in an interview with The Wall Street Journal. “Both sides agree that there has to be significant progress, meaning a feeling that they’re very close before that happens.”

“We’re not there yet. But we’re closer than we’ve been for a very long time,” he added.

Trump administration officials have expressed some hope that a summit could happen by the end of this month or in early April.

The collapse of the second summit between Trump and North Korean leader Kim Jong Un may also have increased the perceived risk of Xi making a trip to Florida for a “signing ceremony.” An event with the same title had been penciled into Trump’s official schedule on his visit to Hanoi to meet with Kim.

In that case, working groups failed to finalize the details of an agreement before the two leaders met, leaving little time for further negotiations and ultimately setting the summit up for failure.

While China runs the risk of Xi leaving a summit empty-handed if details are not nailed down, Branstad said that US officials want there to be some flexibility.

Trump administration negotiators want “the agreement pretty much worked out, and maybe a few final touches or final things resolved by the two leaders.”

“It has been a long and difficult process,” Branstad said, adding: “I’m more hopeful now than I’ve been throughout the last year that we can see an effective agreement reached.”

The ambassador also chimed in on the issue of US criminal cases brought against Chinese telecoms firm Huawei and its chief financial officer Meng Wanzhou.

“It is really a separate issue and it’s really in the hands of the Southern District of New York, certainly not with the president,” Branstad said.