The Democratic Senatorial Campaign Committee (DSCC) outraised its GOP counterpart in May, but the National Republican Senatorial Committee (NRSC) paid off its debt, becoming the first campaign committee of the cycle to do so.

Both parties are competing hard for control of the Senate. Republicans only need four seats to win the majority (if President Obama wins reelection). Dems are defending 23 seats while Republicans are defending 10.

For the month of May, the DSCC raised $4.1 million, compared to the NRSC's $3.08 million.

The Dems fared much better than the $2.8 million they raised in April, and credited that to their criticism of the Republicans' budget proposal, which contains a controversial provision to turn Medicare into a voucher-like system for those under the age of 55.

"The game changer this last month was the Republican plan to end Medicare. It is helping motivate Democratic donors in every corner of the country, helping us outraise the Republicans and surpass our own fundraising goals," said DSCC executive director Guy Cecil.

Republican fundraising was down a bit from its $3.4 million in April, but the NRSC became debt-free in May, paying off the last $1 million it owed. It's common for committees to go into debt during an election cycle and to pay it off the following year.

“Strengthening the NRSC’s finances has been a top priority for Sen. [John] Cornyn [R-Texas] since the moment he took this job, and we’re pleased to be the first national committee to be debt-free this cycle. Every dollar raised will go directly to winning back a Senate Republican majority in 2012," said Brian Walsh, the NRSC communications director, in a statement.

Last cycle, the NRSC also paid off its debt in May, but it got a $2 million transfer from the Republican National Committee to do so.

The DSCC did not respond to a question about how much debt it's carrying, but, as of the end of April, it was $4.35 million in debt, according to its Federal Election Commission filing.

Paying off its debt left the NRSC with less cash on hand than the Dems. Republicans have $1.77 million versus the DSCC's $7.8 million.

The DSCC has raised $18.62 million thus far this year, while Republicans have raised $17.74 million.