(CNN) - 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."
Crist, the popular GOP governor who is mounting a bid for Senate and has won the endorsement of the National Republican Senatorial Committee, finds himself locked in a tight race with Rubio, the former Florida House Speaker.
Once little known throughout the state, Rubio steadily climbed in the polls as he embraced the mantle of fiscal conservatism and painted Crist as a moderate too willing to spend taxpayer dollars.
But referencing a recent report that Rubio used a Florida Republican Party credit card for personal expenditures, Crist dubbed him "one of the most irresponsible spenders I've ever seen."
"He talks about how we need to spend less in Washington, but he sure seems to like spending other people's money," he told the Web site.
Rubio spokesman Alex Burgos called Crist's claim of frugality the governor's "latest reinvention."
"When he endorsed and campaigned for the $787 billion stimulus, Floridians saw firsthand how Charlie Crist's personal frugality does not translate into fiscal restraint with taxpayer money," Burgos said.