GWEN IFILL:

The ever-growing cost of political warfare is now reaching into the stratosphere, with the 2016 election on track to possibly double the roughly $2 billion spent in 2012.

Part of the reason for all that spending has been the rise of millionaire and billionaire political activists on both sides of the political aisle. In the past, we have looked at the Koch brothers, who have pledged nearly a billion dollars to Republican and conservative causes this cycle. On the left, there is billionaire Tom Steyer, who has pledged millions on the issue of climate change.

And Tom Steyer joins me now.

Welcome to the NewsHour.