By Niels Lesniewski and Thomas McKinless

“Every once in a while I am ready to do a ‘McCain’ on these guys,” Sen. Claire McCaskill said Wednesday, summing up her level of frustration with the operators of Backpage.com, a classified ad website that’s become infamous as a marketplace for human trafficking. Sen. John McCain, the Arizona Republican known at times for his temper, said after the Missouri senator’s quip that ”someone is calling the kettle black.”