U.S. Senator Scott Brown's campaign for reelection brought in roughly $5 million in political donations during the second quarter of 2012—nearly $1.6 million more than the Republican raised in the first quarter—his campaign announced Wednesday evening.

Brown's second quarter total, while larger than that of almost any other Congressional candidate in the country, was not enough to outraise his Democratic rival, Harvard Law School professor Elizabeth Warren, who brought in $8.67 million during the same period. The Brown camp said that quarter two funds have left the incumbent Republican with $15.5 million cash on hand—about $2 million more than Elizabeth Warren has at her disposal.

"This election will be decided by the voters of Massachusetts based on two very different visions for our future, and Scott Brown will have the resources he needs to share his pro-jobs message and independent record with voters across the Commonwealth," Brown's campaign finance director John Cook said in a statement.

Where the campaign contributions came from is still unclear. Candidates do not officially have to file with Federal Election Commission until Sunday, meaning that lists of itemized contributions and expenditures will not be available for some time. That lag, however, did not keep the two camps from calling into question the other's funding.

"Professor Warren may have the support of the out-of-state, left-wing interest groups, but no amount of money can change the fact that she supports job-destroying tax hikes that would crush our struggling economy."

Two-thirds of the $5 million raised by Brown's campaign in April, May, and June came from within Massachusetts, his campaign said. Warren's campaign did not release such a figure, but said that over 40,000 Bay State residents had contributed to the Democratic campaign.

"So far, more than 40,500 residents of Massachusetts have donated to Elizabeth's campaign and more than 80 percent of her donations are $50 or less. Her proven record of standing up for middle class families is building strong grassroots support across the Commonwealth," wrote Alethea Harney, Warren's spokeperson, in a statement.

As analysts have predicted, both candidates have raked in money at a record pace. Brown and Warren have combined raised a little more than $40 million already, with four months remaining until election day.

A recent poll by Public Policy Polling showed Brown and Warren tied with 46 percent of the vote respectively.

—Staff writer Nicholas P. Fandos can be reached at nicholasfandos@college.harvard.edu.