Let C=total number of immigrants – legal and illegal – who annually enter the U.S. under existing laws.

Let F=the total number of immigrants who would annually enter the U.S. under open borders.

Under perfectly open borders, C=F.  Under perfectly closed borders, C=0.  Where does the status quo fall on this continuum?  The obvious metric:

Open Borders Index=C/F

With closed borders, the Open Borders Index=0.  With open borders, the Open Borders Index=1.

Regardless of your views on immigration, it’s hard to see how your estimate of the actually existing Open Borders Index could exceed .05.  After all, there are hundreds of millions of people who would love to move to the U.S. just to shine our shoes, and three million would be a very high estimate of annual legal plus illegal immigration.  Rhetorical invective notwithstanding, mainstream immigration policy proposals are all in the neighborhood of .01 to .05. 

Lessons: If, like me, you want to set the Open Borders Index=1, you should be utterly depressed.  Nothing close to open borders is even on the table.  If, however, you want to set the Open Borders Index=0, rejoice.  We’re approximately there already.