Locked in the nation’s most expensive Senate race, Senator Scott Brown and Democratic challenger Elizabeth Warren both revealed shrinking campaign war chests late Thursday night, with about $3.7 million left for the Republican candidate and $3.5 million left for the Democrat.

The latest reports covered fund-raising between Oct. 1 and Oct. 17. Warren, who has outraised Brown in every reporting period, raised $2.5 million in the first half of October. Brown, who is also among the nation’s leading fund-raisers, collected $1.6 million over that period.

But in the final weeks of the campaign, both candidates are spending far more than they are taking in, hoping to close out the tight election with a blitz of ads. Brown reported spending $8.3 million in just over two weeks’ time, while Warren reported spending $6.3 million.

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The candidates have been a constant presence on television. Warren, since entering the race last year, has raised $38.8 million. Brown has raised about $29 million since he took office January 2010. In addition, he has carried over $7 million from his 2010 special election. Total it all up and it’s about $75 million.

Both candidates have large staffs and have spent millions of dollars on polling, consultants, yard signs, food, and anything other necessities of a modern campaign.