The prospect of a Donald Trump nomination is accomplishing what a diverse and talented field of Republican presidential contenders could not: uniting the party’s big-money donor establishment.

Some of the wealthiest conservative givers in the country are helping pay for a series of last-ditch attacks to wound Trump, disclosures filed on Sunday night revealed, even after previously backing rival Republican candidates. And officials involved with the political groups have made clear that they are aggressively raising more money to fight Trump, hoping to deprive him of enough delegates to win the Republican nomination outright. That would set the stage for a contested convention in July.

Big money being spent

Our Principles PAC, a group set up to highlight Trump’s past liberal positions, took in $4.8 million last month, with a roster of donors that shows it has significantly expanded beyond the Ricketts family, which provided the group’s early funding.

Beyond the Rickettses, who collectively provided another $2 million to the group, Our Principles raised $500,000 from William E. Oberndorf, a California investor who had previously backed Jeb Bush, and $100,000 from Harlan Crow, a Texas real estate developer, who had supported Sen. Marco Rubio of Florida. Our Principles also raised $1 million from Warren Stephens, an Arkansas investment banker who gave large checks to “super PACs” backing four candidates who have since quit the race.

'Now they are uniting'

The stream of new money confirms that the Republican Party’s financial elite — who put hundreds of millions of dollars behind more conventional presidential candidates, only to watch almost all of them falter — believes that a focused and well-financed attack campaign could still halt Trump in his march toward the party’s nomination.

“You have all these people who backed different candidates, and now they are uniting,” said Brian Baker, a political adviser to the Ricketts family. “These are people who backed Senator Cruz, Governor Kasich, Governor Christie, Senator Rubio — all stripes. And they are all conservatives.”

A million here, a million there

Stephens and his brother also gave $2.5 million last month to a super PAC connected to the Club for Growth, a free-market activist group that was one of the first outside organizations to take on Trump. All told, the group, whose members met last week to discuss how to escalate their efforts against Trump, raised $4 million in February, three times as much as it had raised any other month this election cycle.

Richard Uihlein, an Illinois shipping-supplies manufacturer and conservative activist, who backed Gov. Scott Walker’s campaign last year, gave the Club for Growth $500,000. Several other donors with ties to Republican also-rans gave large contributions as well, including Richard Gaby, who gave $50,000 to a super PAC backing former Gov. Bobby Jindal of Louisiana, and Robert Arnott, a California-based investor who has poured hundreds of thousands of dollars into groups backing Sen. Ted Cruz of Texas. In January, the group also raised $100,000 checks from other prominent donors allied with Trump’s rivals, among them Robert Mercer, a longtime Club for Growth donor who is backing Cruz.

Koch donors involved

Some of the new money is coming from donors to the political network led by Charles G. and David H. Koch. Their network, the biggest and deepest-pocketed independent political force in the conservative world, has for months weighed intervening in the Republican primary against Trump.

But some of their donors have come off the fence: Those backing Our Principles include Stan Hubbard, a Minnesota radio and television station owner, and Tom Rastin, an executive at an Ohio-based firm that manufactures hydrofracking equipment.

Rastin also contributed $300,000 to an independent group backing Gov. John Kasich of Ohio.

A hint of how much more money the anti-Trump groups may be able to raise going forward could be found in disclosures filed Sunday night by Conservative Solutions, a super PAC that backed Rubio until he dropped out of the race on March 15.

$25 million raised in one month

In February, as Trump began racking up critical victories in early primary states, prominent donors poured $25 million into Conservative Solutions, a huge amount for a single month.

Its top contributors included Leonard Blavatnik, a Russian-born, London-based American investor whose holdings include Warner Music; Ronnie Cameron, an Arkansas poultry magnate who previously backed Mike Huckabee, and companies linked to Maurice Greenberg, the insurance executive and prominent Republican donor.

Figures reported on Sunday now suggest that Cruz is the sole remaining Republican candidate with the financial wherewithal to challenge Trump. Cruz raised $11.9 million in February and, despite burning through $17.5 million over the course of the month, began March with $8 million in cash on hand. He also continued to raise substantial amounts of money from small donors, who can give repeatedly without hitting the contribution limit of $2,700. And a constellation of super PACs backing Cruz began March with more than $20 million in cash on hand.

Trump reported raising and spending about $9 million during the month, most of it money he lent to his campaign. Kasich reported having just $1.3 million in cash on hand at the beginning of March.