WASHINGTON — Every day more than $4 billion worth of goods cross the United States’ borders with Canada and Mexico. …Much of this bustling cross-border commerce is duty-free, thanks to the US-Mexico-Canada Agreement, or USMCA, that President Trump negotiated with America’s northern and southern neighbors during his first term. But the future of the USMCA , which took effect July 1, 2020, is cloudy as the three countries begin what could be a tempestuous attempt to renew the pact this year. The United States is demanding changes to the treaty. …Trump also suggested last fall that the United States could negotiate separate deals with Canada and Mexico, ending the three-country North American bloc that previous administrations saw as crucial to competing economically with China and the European Union. The talks kick off Monday between US and Mexican trade officials. …At stake is $1.6 trillion worth of annual trade in goods.