The president-elect’s opening salvo in trade and border talks with the United States’ neighbors is casting a harsh light on the North American alliance.

“Right now, I see everything that Trump’s doing on tariffs as a negotiating tool,” said Sen. Chuck Grassley (R-Iowa), who saw farmers in his home state negatively impacted by retaliation from Trump’s first trade war with China. “And we’ll have to wait and see how successful he is about that.”