What key fact contributes to the volatility of immigration in public discussions and political debate in the united states today? the united states has secure borders. the united states is a nation of immigrants. the united states openly defies how the united nations defines immigration. the united states defines immigration in an odd manner.

I believe the answer is:  The United States is a nation of immigrants.

This divide the main opinion regarding this matter into two main point of views.
On one side, they believe that immigration to united states should be left open since it's the foundation in which the economy of this country was built.
On the other side, they believe that immigration should be restricted since it took away a lot of job opportunities for poor people.