Fredreka Schouten

USA TODAY

Members of the family that owns the Chicago Cubs have ponied up more money in their effort to slow Donald Trump's march to the Republican presidential nomination.

TD Ameritrade founder J. Joe Ricketts and his wife Marlene Ricketts donated a combined $2 million in February to Our Principles PAC, a super PAC that has blistered Trump on the airwaves as a con artist. Marlene Ricketts had provided $3 million to the group in January, virtually all the money the super PAC raised during its first month of operation. (Her donation prompted Trump to warn on Twitter that the family had better "be careful.")

However, the Ricketts clan is no longer alone in its battle with Trump.

Billionaire hedge-fund founder Paul Singer and Arkansas-based financier Warren Stephens each gave $1 million to the PAC last month, according to a report the group filed Sunday evening with the Federal Election Commission. In all, the group brought in nearly $4.8 million from 17 donors last month.

Singer, one of the Republican Party's most active fundraisers, supported Florida Marco Rubio's failed bid for the presidency. Stephens, also a longtime GOP donor, had contributed to a super PAC aiding former Florida governor Jeb Bush's unsuccessful White House campaign.

Six-figure donors to the super PAC last month included San Francisco-based financier Bill Oberndorf and Dallas real-estate magnate Harlan Crow.

Our Principles PAC has continued to collect money aggressively in March, although those donors' identities won't be known until next month. Separate filings that chart the group's day-to-day advertising spending show the PAC already had spent $11.7 million through early last week to oppose Trump, who continues to dominate the GOP presidential race.

The group announced Friday that it was running a new round of anti-Trump ads in Utah ahead of the state's GOP caucuses Tuesday. One ad, called "Imagination," uses clips of a speech by the GOP's 2012 presidential nominee Mitt Romney, denouncing Trump. Trump's foes believe the ad will resonate with Utah voters, many of whom share Romney's Mormon faith.

Romney previously had announced he would support Texas Sen. Ted Cruz in Utah as part of a bid to deny Trump the 1,237 delegates he needs to clinch the nomination.