The Democratic Congressional Campaign Committee is making its first significant independent expenditure in the special election to succeed Rep. John Murtha (D-Pa.).

The committee’s IE arm bought $136,000 in TV ad time to boost Mark Critz, a top Murtha aide running to succeed his boss in the May 18 special election. The DCCC ad comes in response to the National Republican Congressional Committee’s $273,000 investment in the race earlier this week.

The NRCC ran a negative spot targeting Critz, and now the DCCC is running a negative spot against businessman Tim Burns, the GOP nominee.