Within minutes of Jeb Bush dropping out of the presidential race Saturday night, some of his donors were preparing to throw their financial support behind Marco Rubio, who has emerged as the strongest candidate among the establishment wing of the party.

"Jeb's network is already naturally migrating to Marco," said Gaylord Hughey, a top Bush fundraiser from Texas, echoing what four other top donors told Reuters. "It's the clear path."

"It's a stampede," added another donor, who spoke on the condition of anonymity because he wanted to give Bush some time after dropping out before he went public with his support of Rubio, the U.S. senator from Florida.

Three other Bush donors, who declined to be named, also said they now planned to support Rubio.

Although he has failed to win any of the first three nominating contests, Rubio is considered by many political strategists as the best positioned to challenge frontrunner Donald Trump, a billionaire political outsider, and Senator Ted Cruz of Texas, who has campaigned on an anti-Washington message.

The likelihood that some of Bush's deep-pocketed donors will back Rubio comes at an opportune time for his candidacy, as he heads into a series of contests in March that will be crucial for building momentum.

Brian Ballard, who raised money for Bush last year but switched allegiances last summer to Rubio, said: "It's flooding tonight. Ninety-five percent of Jeb's money is going to end up with Marco."

Rubio had only $5 million in cash on hand at the end of January, federal campaign finance reports released Saturday night show, a slim buffer by modern campaign standards.

Conservative Solutions, a political spending group that supports his campaign, had $5.6 million on hand at the end of January, but spent an additional $9.3 million on advertising in the first 19 days of February.

By contrast, Right to Rise, Bush's political spending group, had $24.5 million on hand at the end of January but spent $6.6 million of that in February on ads. And his network of donors have proven their financial might, helping Bush at one point to amass a war chest of $150 million.