What is a major political issue between the US and Mexico?

One of the major political issues between the United States and Mexico is immigration. The US-Mexico border is the most frequently crossed international border in the world, and it has been a source of tension between the two countries for many years. The United States has a long-standing policy of严格的移民控制, and it has built a wall along some parts of the border in an effort to prevent undocumented immigration. Mexico, on the other hand, has a more relaxed immigration policy, and it has been critical of the United States' approach. The issue of immigration is likely to continue to be a source of tension between the United States and Mexico for many years to come.