In 2003, Dan Sullivan, then a White House national-security staffer, was in the Oval Office when China’s vice premier promised President George W. Bush the country would fix intellectual property theft. It didn’t.

In 2015, Mr. Sullivan, now a freshman Republican senator from Alaska, watched Chinese President Xi Jinping promise President Obama that China wouldn’t steal trade secrets through cyberhacking or militarize the South China Sea. “Has China kept these commitments? No,” Mr. Sullivan declared on the Senate floor earlier this month.

Today, Mr. Sullivan says, President Trump can succeed where Mr. Bush and Mr. Obama failed: in achieving structural changes in China’s laws, economy and behavior. “I give the president credit for getting us to this point right now,” Mr. Sullivan said in an interview.

The question is, will Mr. Trump stand his ground? Mr. Bush and Mr. Obama failed in part because they cared about other matters more than whether China kept its promises: countering North Korea and Iran’s nuclear ambitions and combating the global financial crisis and climate change. This made them reluctant to punish China except through World Trade Organization-approved rules.

By contrast, Mr. Trump entered office determined to stop what he considered unfair practices that inflated the U.S. trade deficit; he cared little about alliances and the WTO. After initially prioritizing China’s help on North Korea, he imposed tariffs and threatened to raise them further if China doesn’t satisfy U.S. complaints by March 1. The Justice Department stepped up investigations of wrongdoing by Chinese companies, in particular telecom-equipment manufacturer Huawei Technologies Co.