The main donor of a super-PAC designed to destroy Republican presidential front-runner Donald Trump’s campaign has been exposed after spending $4 million on attack ads against the candidate.

Called “Our Principles PAC,” the organization is mostly funded by Marlene Ricketts, the matriarch of the Ricketts family that owns the Chicago Cubs baseball team.

Ricketts has so far contributed $3 million to the super-PAC which is being run by former Mitt Romney adviser Katie Packer.

Our Principles PAC has spent more than $4 million running attack ads against the GOP front-runner in Iowa, New Hampshire, and South Carolina, which hosted the first presidential primaries and caucuses.

Packer said in late January that the organization will get its messages before nearly every Republican voter in the states.

Despite the significant spending, however, the real estate mogul has had strong performances, winning by a large lead in South Carolina and New Hampshire and finishing Iowa at the second place.

According to the Federal Election Commission, almost all the money used by the only serious anti-Trump group to date came from Ricketts, whose identity was first reported by The New York Times.

The family had previously given $5 million to a super-PAC supporting the failed presidential bid of Wisconsin Governor Scott Walker.

Ricketts are yet to fully endorse another presidential candidate, but clearly they like both Texas Senator Ted Cruz and Senator Marco Rubio of Florida, as in June last year, Marlene Ricketts donated $10,000 to super-PACs supporting Rubio and Cruz.

Besides a token $250 donation, the only other wealthy donor to the anti-Trump organization in January was Illinois businessman Richard Uihlein, who paid only $7,500.

Interestingly, Uihlein had also given $2.5 million to Walker’s super-PAC, but after the Wisconsin governor quit the race he endorsed Cruz, contributing $1 million to a pro-Cruz super-PAC.