Wealthy donors handed over $25 million US last month to an outside group backing then Republican presidential candidate Marco Rubio, and the flood of money helped pay for thousands of television advertisements.

Rubio-aligned Conservative Solutions PAC aired more than 2,300 commercials since Super Tuesday on March 1, according to Kantar Media's campaign analysis group. The political action committee was expected to shell out $9.6 million US on radio and TV by March 15.

It still wasn't enough.

Rubio, a Florida senator, ended his bid after an embarrassing loss to Donald Trump last week in his home state.

The presidential candidates — current and former — must file their February campaign finance reports to the Federal Election Commission on Sunday, as they look ahead to the next series of nominating contests in Arizona, Idaho and Utah on Tuesday.

Going broke for Rubio

Conservative Solutions raised about $58 million in support of Rubio since he became a candidate last spring. More than 40 per cent of that money arrived in February alone, new fundraising reports show.

Many of the donations came from donors whose favourite candidates had previously failed. In fact, the pro-Rubio surge was concentrated in the days after one-time rival Jeb Bush, a former Florida governor, dropped out Feb. 20.

A make-or-break evening for some presidential candidates as both Republican and Democratic voters headed to the polls in five different primaries 2:30

Poultry magnate Ronald Cameron was Conservative Solution's top donor in February, contributing $5 million. Cameron, the chief executive officer of Little Rock, Ark.,-based agricultural company Mountaire, had previously given $3 million to a group backing former Arkansas governor Mike Huckabee, also once a 2016 presidential hopeful.

The insurance executive Hank Greenberg's C. V. Starr & Company, Inc. and Starr International companies gave a total of $5 million to Conservative Solutions. Last year, C.V. Starr gave $10 million to a group backing Bush, the former Florida governor.