Throughout the campaign season, Trump has pledged that he would label China a “currency manipulator” on his first day of office, arguing that the country “keeps the yuan artificially weak against the dollar to make its exports more competitive, at the expense of manufacturing jobs in the U.S.”
President Trump would only have to direct his Treasury Department to designate China a currency manipulator. This action would not require any approval from Congress (though Trump’s Secretary of the Treasury nominee would have to be approved by the Senate). According to Trump, this would then:
“… trigger a series of actions that will start the process of imposing countervailing duties on cheap Chinese imports, defending American manufacturing and preserving American jobs. Add to these actions direct and focused protection of intellectual property…”
Trump can do all of this -- impose high tariffs, withdraw from trade agreements, etc. -- without the approval of Congress. Of course, those within his administration, from congress, US companies could appeal to the Supreme Court, and the Supreme Court could evaluate the constitutionality of these executive actions.