Our Principles PAC, a newly formed super PAC set up by a former top aide to Mitt Romney, is set to begin airing a TV ad in Iowa that calls into question his devotion to conservative positions — and asks Iowa voters bluntly, “How much do we really know about Donald Trump?”

The ad, which invokes Trump’s past statements on hot-button issues like abortion and health care, marks one of the most aggressive efforts yet to take down the billionaire businessman, who leads most state and national polls and is in a competitive battle with Ted Cruz in Iowa.

Katie Packer, who served as Romney’s deputy campaign manager in the 2012 election and who now heads Our Principles PAC, declined to give an exact figure for how much the anti-Trump group was spending to air the commercial, though a source familiar with the TV buy said it was in the “seven-figure” range.