Hello there!
The North American Free Trade Agreement, as known as NAFTA, was created mainly for business and trading reasons as it name states. The United States, Canada and Mexico agreed to have a free commercial zone between their countries, and all the information exchanged relating negotiations must remain confidential.
The United States has always had a huge impact on Mexico's economy, as they share a highly integrated economic relationship. The United States provides the largest amount of direct foreign investment in Mexico, and lots of Mexican entrepreneurs invest on the U.S. If the U.S. economy starts falling, Mexico's economy will be falling too due to its largest economy negotiations and trades, and also due to their closeness between each other. They tend to share more relations, not only economic. The relationship between the U.S. and Mexico has become larger over time, incorporating cultural, musical, economic, familial, political, and security relationships beneficial to both countries and its citizens.
So, if the U.S. shows a weak economy, Mexico will be suffering it too.