Hillary Clinton recently announced that she was setting up a new group called Onward Together, offering few details other than that it will support an array of progressive causes, such as Swing Left, Emerge America, Color of Change, Indivisible and Run for Something. Unlike the Clinton Foundation, which is a charity, Onward Together will operate as a social welfare organization.

But what exactly are social welfare nonprofits, what’s the difference between them and charities and how involved in politics can they get?

As a law professor who formerly served as counsel to the nonpartisan congressional Joint Committee on Taxation, I am interested in the use of nonprofits to serve political purposes. I would like to explain why this kind of organization has become more popular – and more controversial.

What are social welfare organizations?

Social welfare groups are nonprofits formed to benefit the community in some way.

The largest social welfare groups, like AARP, the National Rifle Association and the local units of the NAACP, are familiar to most Americans. Smaller ones, such as firefighters’ associations, neighborhood civic associations and many PTAs serving specific schools, are more common. According to the National Center for Charitable Statistics, there are more than 83,000 social welfare nonprofits.

Social welfare organizations, sometimes referred to by the part of the tax code regulating them – section 501(