The Democratic Senatorial Campaign Committee outraised the National Republican Senatorial Committee in July, pulling in $4.4 million to the NRSC's $4.2 million.

The DSCC had $22.4 million in the bank heading into the final stretch of campaign season before Labor Day, compared to the NRSC's $21.1 million, but the DSCC has been spending more heavily on field operations throughout the year. In July, the DSCC spent $3.5 million to the NRSC's $2.6 million.

"Even though Republicans have enjoyed a hospitable political environment, Democrats continue to outraise them and hold a cash-on-hand advantage," said DSCC spokeswoman Deirdre Murphy. "The committee and candidates are all in strong positions to wage competitive races in each of our targeted races, including many red seats."

Two years ago, when Democrats added to their new Senate majority, the DSCC had $42.9 million in the bank at this point in the cycle compared to the NRSC's $25.4 million, leading Democrats to suggest that the GOP will have a harder time winning as many of their targets as polls indicate they should.

But the NRSC has more opportunities to gain seats than the DSCC had then, said NRSC Executive Director Rob Jesmer. "Republicans are now on offense in at least 12 Democrat-held Senate seats, and the wind is at our backs moving towards November as more Americans stand up and demand checks-and-balances in Washington," he said.