Former state Treasurer Barbara Hafer (D) has dropped out of the race to succeed the late Rep. John Murtha (D).

According to a source close to Hafer, she did not have enough signatures out of the 1,000 required to withstand a legal challenge.

Her decision means that former Murtha aide Mark Critz ­­— the Democratic nominee in the special election to fill the rest of the current House term — will only face Navy veteran Ryan Bucchianeri for the nomination for the full House term that begins in 2011.

On Thursday, Republicans will pick their special election candidate, either 2008 GOP nominee Bill Russell or businessman Tim Burns.