Republican presidential candidate Marco Rubio pauses during a speech to voters at the Northwest Iowa Republican rally at Northwestern College in Orange City, Iowa, on Friday.

One of the wealthiest and most influential Republican donors is throwing his support behind the presidential campaign of US Senator Marco Rubio of Florida, the New York Times reported on Friday.

Billionaire New York investor Paul Singer sent a letter to dozens of other donors on Friday declaring his support for Rubio in a major blow to the struggling campaign of former Florida Gov. Jeb Bush, the newspaper said. They are among the candidates seeking the 2016 Republican presidential nomination.

Asked by reporters in Iowa about Singer’s support, Rubio said: “When people donate to us, they buy into our agenda, and I’m glad that he has and it will help us with resources.” Rubio added: “Resources alone are not enough … but we’re grateful to have his help, obviously.”

Rubio, Bush, New Jersey Gov. Chris Christie and several other Republican candidates had eagerly sought Singer’s support, the Times said.

In the letter, Singer described Rubio as the only candidate who can “navigate this complex primary process, and still be in a position to defeat” Hillary Clinton, the front-runner for the Democratic presidential nomination in the November 2016 general election.

Singer gave more money to Republican candidates and causes last year than any donor in the country, the Times said, citing the Center for Responsive Politics.

He is courted by Republicans both for his willingness to give and for his network of fellow conservative donors, the newspaper reported.

The Times did not say how much Singer intended to donate to Rubio, who is coming off a strong debate performance on Wednesday night in Colorado.

Rubio is third behind businessman Donald Trump and retired neurosurgeon Ben Carson in a Real Clear Politics average of national opinion polls for the Republican race.

Bush, who is in fifth place in the polling and recently downsized his campaign staff, gave what is widely viewed as a lackluster performance in the debate.

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