Joe Sestak is challenging Arlen Specter — and this time it’s official.

Sestak, a two-term House member, held a formal announcement event Tuesday morning to say that he will wage a Democratic primary campaign against Specter, who switched parties in April and is seeking a sixth Senate term as a Democrat.

Sestak told supporters that the electorate voted for “change” with his election to the House in 2006 and Barack Obama’s election as president in 2008, and that Pennsylvania voters in 2010 “will vote for a change and accountability.” He promised to be the “hardest working senator.”