BEIJING — After decades of deriding China as a lousy copycat, the United States now fears China’s rapid rise as a technology powerhouse and sees it as a major — even existential — threat to U.S. dominance. The Trump administration has waged an escalating trade war against China under the pretext of punishing Chinese transgressions such as forced technology transfers, predatory licensing practices, cyber theft of intellectual property and the state-sponsored acquisition of American tech companies.