House Republicans have long argued that one of the reasons Democrats consistently show more cash on hand in monthly fundraising reports is because the GOP is on a more back-loaded fundraising calendar.

But it’s getting pretty late in the cycle to make up a $16.6 million difference, and it’s not like Republicans haven’t been trying. The Democratic Congressional Campaign Committee began June with $28.6 million in the bank while the National Republican Congressional Committee had $12 million.

May fundraising reports filed this week show that the NRCC paid more than $870,000 to fundraising telemarketing firm InfoCision during May.

An NRCC source acknowledged Monday that significant money is being invested in using mail and phone calls to prospect for donors because of an increase in favorable responses.

But Republicans believe they will start making an even bigger dent in the DCCC’s cash lead in the coming months with the launch of the biennial “Battleground” fundraising program, which kicked off last week and has a goal of getting Members to donate a total of $20 million to the committee by mid-September. The NRCC said last week that it had already collected $5 million in early donations for that effort.

Meanwhile, both committees spent heavily during a month in which key special elections in Pennsylvania and Hawaii were held.

The NRCC spent $477,000 on independent expenditures in May while the DCCC spent $508,000 on IEs. The Democratic committee also transferred $50,000 to the Pennsylvania Democratic Party about a week after the hard-fought special election to fill the seat of the late Rep. John Murtha (D). Eight days before the election, the DCCC transferred $75,000 to the state party.

The DCCC, which dropped independent expenditures in the Hawaii special election early before pulling out when local party leaders were unable to unite behind one candidate, sent just $1,500 to the Hawaii Democratic Party in the days after losing the seat.

The NRCC raised $5.4 million while spending $4.8 million in May. The DCCC raised $5.1 million and spent about
$3.8 million. Since the start of the cycle, the DCCC has raised about $84.6 million to the NRCC’s $66.4 million.

Meanwhile, the Senate campaign committees entered the final stretch of the 2010 cycle neck and neck in the money chase.

The Democratic Senatorial Campaign Committee outraised its GOP counterpart during the month of May by $1.4 million, but the National Republican Senatorial Committee ended last month with more in the bank for the first time since April 2009.

The NRSC brought in $3.6 million, bringing the committee’s cash-on-hand total to $18.1 million at the end of May. GOP Sens. Susan Collins (Maine) and Lisa Murkowski (Alaska) both contributed $15,000 to the committee during the month. The NRSC spent $2.5 million but had no independent expenditures on races.

The DSCC raised $5 million, spent $4.6 million and had about $17.6 million in cash on hand as of May 31.

The NRSC’s monthly receipts in May were down from the $4.4 million raised in April and the $5.1 million raised in March. Over the course of the cycle, the GOP Senate committee has raised $64.1 million. The DSCC raised $6 million in March and $4.2 million in April, and it has brought in about $66.8 million for the cycle.