Rep. Mark Critz, D-Pa., reenacts his swearing-in Thursday on Capitol Hill in Washington. He won a special election Tuesday to replace the late John Murtha.

WASHINGTON — Democrats on Thursday welcomed Mark Critz to their ranks after he dashed Republican hopes of capturing a Pennsylvania House seat seen as a possible bellwether for the midterms.

House Speaker Nancy Pelosi, D-Calif., swore in Critz after he won a special election to fill the final months of the late Rep. John Murtha's term. The longtime Murtha aide beat Republican Tim Burns on Tuesday. Both candidates will meet again this fall.

"This moment is bittersweet for me," said Critz, recalling his former boss who died in February at age 77 from complications of gallbladder surgery.

Murtha had held the seat for 36 years, but Republicans were counting on opposition to congressional Democrats and tea party-driven discontent to carry them to victory.

Critz stressed his ties to his old boss, who as chairman of a House Appropriations panel steered millions of federal dollars to his district.

Critz benefited from a key endorsement from Murtha's widow, Joyce Murtha, who was on hand for the swearing-in ceremonies.