There has been a good amount of discussion on the presidential campaign trail about the issue of college affordability and student loan debt.  I have written in previous blog posts about some of Hillary Clinton’s proposals, as well as those of Martin O’Malley.  This week, I wrote a column for the website The Conversation, where I described why any discussion of college affordability needs to start with the role of Pell Grants, the foundation of the federal government’s student aid programs.