The U.S. is pushing for a trade deal with China that includes “significant structural changes” to the Asian nation’s economic model, as well as provisions that ensure Beijing keeps its promises, President Donald Trump’s top trade negotiator said.

It’s still too early to tell if China will concede to U.S. demands, said U.S. Trade Representative Robert Lighthizer, with plans underway for Trump to invite his Chinese counterpart Xi Jinping for a summit to finalize a potential agreement. Lighthizer’s comments contrast with Trump’s more optimistic remarks this week when he raised hopes for an imminent deal.

“This administration is pressing for significant structural changes that would allow for a more level playing field -- especially when it comes to issues of intellectual property rights and technology transfers,” Lighthizer said Wednesday in testimony before the House Ways and Means committee.

The issues on the table between the U.S. and China “are too serious to be resolved with promises of additional purchases,” said Lighthizer, who is leading the negotiations for the Trump administration. “We need new rules.”

Striking a broad trade agreement with China won’t be a one-off event, said Lighthizer, adding that negotiations will likely continue to address other problems that will pop up.

Big 'If'

“If we can complete this effort -- and again I say ‘if’ -- and can reach a satisfactory solution to the all-important outstanding issue of enforceability as well as some other concerns, we might be able to have an agreement that turns the corner in our economic relationship with China,” he said. “Much still needs to be done, both before an agreement is reached, and more importantly, after it is reached.”

The U.S. is “very aware of the history of our trading relationship with China, and the disappointments that have resulted from promises that were not kept,” he added.

Trump this week raised the prospect that he could sign a new trade deal with Xi, as both sides expressed optimism following the conclusion of the latest round of talks. Treasury Secretary Steven Mnuchin said this week that a leaders’ meeting for late March at Trump’s Mar-a-Lago resort in Florida is being tentatively planned.

China Role

Trump’s hint at a deal-clinching summit with Xi underscores the sense that the two nations are approaching an agreement, more than seven months since the U.S. first imposed tariffs on Chinese imports, setting off a tit-for-tat conflict that has cast a cloud over the global economy. But with Trump holding another summit with North Korean leader Kim Jong-Un this week in Vietnam -- a diplomatic effort in which China will play a critical role -- the risk of a setback remains significant.

Trump will have to sell any deal he signs to trade hawks who brought him to power and Democratic lawmakers, who have at times criticized the president for taking his foot off the gas in his efforts to convince China to step up its reforms.

“This administration has chosen to take the path of a high-risk confrontation with China. It must hold out for a good deal, a structural deal,” said Democrat Richard Neal, the chairman of the committee, which oversees trade issues in the House.

Trump has extended a deadline to raise tariffs on Chinese goods beyond this week, citing progress in the latest round of talks that wrapped up Sunday in Washington. The president hasn’t specified how long he’d extend the tariff truce.

China has repeatedly promised to ramp up purchases of American goods including soybeans and energy products.