The drop started with the economic downturn in '08 -- long before Trump's anti-immigration tirades.
An equally silly reading of the data is that Mexicans wanted to live in the US because Bush was president, but they hate Obama so they stopped coming and started leaving.
All signs point to this being economically driven.
It's quite feasible that other criteria (taxes, job creation, etc) contribute more to a candidate's popularity.
Isn't the economy now better than when Bush was the president?
But neither has done much immigration enforcement.
The Mexican economy has done very well over the past 30 years. It started very backwards but finally passed the US economy for the first time in opportunities for many people in 2007. That was partly because of the US crisis. Mexico has continued to grow since then.
That's an extraordinarily precise date for meeting a very vague threshold ("passed the US economy...in opportunities for many people"). What does this mean in concrete terms, and where is the evidence supporting that it was achieved in 2007.