Veteran leaders from both political parties — Iowa Sen. Charles Grassley and former Iowa Gov. and U.S. Agriculture Secretary Tom Vilsack — teamed up at a Des Moines dairy last week to push for quick congressional passage of the retooled trade agreement with Canada and Mexico.

"When everyone thinks that everything in Washington is partisan, this is an opportunity to stress the bipartisan support for this agreement," Grassley said after he and Vilsack toured the Anderson Erickson Dairy on Des Moines’ east...