The GOP field's second-tier presidential candidates didn't raise enough money in the third quarter to keep up with the front-runners.

Former Utah Gov. Jon Huntsman relied on a $2.25 million loan to his campaign for half of the $4.5 million raised since June, third-quarter filing reports show. 

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Former Pennsylvania Sen. Rick Santorum pulled in $700,000, bringing his total to $1.3 million. 

The race's front-runners, Texas Gov. Rick Perry and former Massachusetts Gov. Mitt Romney, each pulled in more than $10 million for the quarter. 

Meanwhile, former Minnesota Gov. Tim Pawlenty managed to raise $929,000 in the third quarter (for a total of $5.4 million) before calling it quits after his third-place showing in this summer's Ames, Iowa, straw poll. Rep. Thaddeus McCotter (R-Mich.) barely raised $61,000 before dropping his bid last month.

For her part, Rep. Michele BachmannMichele Marie BachmannEvangelicals shouldn't be defending Trump in tiff over editorial Mellman: The 'lane theory' is the wrong lane to be in White House backs Stephen Miller amid white nationalist allegations MORE (Minn.) is also reportedly running into fund-raising trouble and is having to rely on costly direct-mail advertising to solicit money. She pulled in $3.9 million in the third quarter and has about $1.3 million cash on hand.