A key NAFTA stumbling block has been the inability to resolve:

Name: A key NAFTA stumbling block has been the inability to resolve:
Brand: Quizplus
Rating: 4.8 (47 reviews)

Question

Quizplus · Accepted Answer

The inability to resolve U.S.-Mexico cross-border truck operations has been a key stumbling block in NAFTA negotiations. Specifically, Mexico has pushed for greater access for its trucks to cross the U.S. border, something that the U.S. has been hesitant to agree to due to safety concerns and protectionist pressures from domestic trucking industry groups.

A Key NAFTA Stumbling Block Has Been the Inability to Resolve