Apparently a number of people have arbitrarily set that value at "one million dollars". (Although technically Bernie's income was not a million dollars, this was the number being put out there which probably also included his assets).
I think as a society we have to revisit these ideas for clarity. Of course, we need to stick to the core principles that people should not gain immense wealth through the exploitation of the poor. We should insist on campaign finance reform and transparency in government to eliminate wealth bias in the control of our government. We should make sure the rich are paying their fair share in taxes, not sheltering it off shore. We should make sure that everyone is treated fairly in the courts and in general regardless of what they have or don't have. We should insist on a society where as long as there is immense wealth, certain things should be a right, like food, shelter, health care and education.
Despite the attempt to create a scandal of Bernie's money, there are few candidates who have so ardently pursued just such a society.