The president of said nation.
The topic is very controversial because there are several viewpoints.
Some people believe that Mexican immigration has become extremely high, and that it must be somehow restricted. Other people may argue that some Mexicans work jobs that most other people would not want to do. Some of these include working on farms or other dirty jobs.
These opposing viewpoints cause the topic of Mexican immigration to be highly controversial.
The correct answer is B. It has caused spending by interest groups to increase. Since the ruling, multi-billion corporations and other interest groups have funneled unprecedented amounts of money to the parties or politicians that are susceptible to further their interests via the Super PACs (that are not allowed to spend money directly in the politicians' campaigns but can spend unlimited amounts of funds independently and in favor of the party/politician of their choice).
