John McCainJohn McCainDemocrats step up calls that Russian hack was act of war McCain: Trump admin must fill State Dept. jobs McCain says he hasn't met with Trump since inauguration MORE's stance on climate change has proven to be controversial with at least one group of economic conservatives, as the Club for Growth today criticized the Arizona Republican's support for a cap-and-trade system.

The concept would set mandatory limits on greenhouse emissions, and allow companies that pollute less to sell their permits to those that pollute more.

"McCain