Lobbying — both in terms of the raw number of people doing it and the money being spent on it — is soaring.  According to a new study by the Sunlight Foundation, lobbying revenue almost doubled between 1998-2012, reaching more than $1 billion by the end of that period.

Lobbyists not allowed. (Patrick Semansky/AP)

That's nothing new. But what is new — and telling — to us is that so much of the growth in the lobbying world comes from people with past experience working within the federal government.

Check out these two charts from Sunlight. The first shows that revenues from lobbyists with no government experience stayed steady over the 14-year period that Sunlight monitored. Revenues for lobbyists with government experience, on the other hand, soared more than 400 percent during that same period.

Image courtesy of the Sunlight Foundation

The second chart details the raw numbers of lobbyists over the past 14 years. Again, the growth in lobbyists comes heavily from those with prior government experience.

Image courtesy of Sunlight Foundation

The trend is quite clear: Those hiring (and paying) lobbyists these days prize previous experience in government above all else. And, of course, "previous government experience" is code for relationships with lawmakers and staff that, at least in theory, opens doors and greases the legislative wheels.

This boom among lobbyists with government experience comes amid efforts in recent years to limit them and their influence.  Senators are currently banned from lobbying their former colleagues for two years and House members have to wait a year until after they leave the chamber to begin lobbying. (Efforts to make that a lifetime ban are going nowhere.)  Staffers face a one-year lobbying ban.  And, the Obama administration is in the midst of a legal battle over its ban on registered lobbyists serving on advisory boards.

The simple fact is that the revolving door between Congress and lobbying is being used far more than ever before. The bans may have slowed the move from public service to private sector but it has done nothing to end it — or even shrink it.