The gloves have been off for a while but Santorum appears to be sharpening his attacks on Romney, while turning to a more populist message.

Politico:

Stepping up his assault on Mitt Romney, Rick Santorum delivered a slashing speech Saturday morning that portrayed the establishment favorite as an elitist and unreliable conservative.

Santorum, appearing before over a thousand conservative activists gathered in suburban Detroit for an Americans for Prospertiy conference, emphasized his immigrant roots, modest background and conservative credentials in an impassioned address that won him a standing ovation.

"I didn't blow in the wind when things were popular with the elite," Santorum said.   "Because I don't come from the elite."

The former Pennsylvania senator was clearly alluding to Romney, who has taken the lead in some polls here.

On taxes, climate change, healthcare and bailouts, Santorum attacked his chief rival by name in what was one of the toughest speeches he's delivered in recent weeks.

"I never thought a Republican presidential candidate would adopt the verbiage of Occupy Wall Street," he said, citing Romney's reference to "the one percent."

Santorum's broadside went beyond issues, though, as he trained his fire at Romney's character.

"What you see today might be something different than what you get tomorrow," the Pennsylvanian said

Later, Santorum added: "He wasn't what he said he was yesterday."

The former senator was notably more energized here than he was in going through a litany of rehashed policy proposals to a modest crowd last night at an event his campaign billed as a major speech.

Asked why he was so tough on Romney, Santorum told reporters after his address: "Fight fire with fire."

Romney started it and if he's not careful, someone else is going to finish it.