Florida Gov. Charlie Crist is stepping up his attacks on Senate primary opponent Marco Rubio, declaring Rubio’s professed conservatism is “the greatest fraud perpetrated on people.”

“I won’t go negative in this race, that’s not my nature, but by the same token, I will not let [Rubio’s] façade continue,” Crist told the National Review Online in comments published Thursday. “When this guy calls himself the real conservative in the race, I’ve got to point out that it’s the opposite.”