U.S. Rep. Jason Altmire, D- Pa., is seen through a window as he votes in the Pennsylvania primary election on April 24 in McCandless, Pa., a suburb north of Pittsburgh. (Keith Srakocic/AP)

Pennsylvania Democrats on Tuesday were dealing with consequences of their 2010 rout as Rep. Mark S. Critz defeated Rep. Jason Altmire in a tough primary battle that pitted two of the most promising members of their delegation against each other.

In the Reading area, Rep. Tim Holden, first elected in 1992 and having survived one bitter redistricting battle 10 years ago, lost to lawyer Matt Cartwright, who had the support of liberal activists who are upset about Holden’s moderate voting record.

But it was the Critz-Altmire matchup that brought home the fallout from the Democrats’ poor showing at the polls two years ago.

Altmire, who beat an entrenched Republican in 2006, was forced into a tough primary battle against Critz, because Republicans got to draw the new district maps after the 2010 Census.

It was Critz’s victory in a May 2010 special election that temporarily allowed Democrats to believe that they may be able hold on to the their majority in the House that November.

Instead, Democrats were bested up and down the ballot, leaving Pennsylvania’s capital dominated by Republicans who redrew the districts to help the GOP.

With the state losing a seat in the House, Republicans put Altmire, 44, and Critz, 50, into a new competitive 12th District that snakes its way eastward from the Ohio border past Pittsburgh and up toward Johnstown. Although Altmire previously represented two-thirds of the district, Critz used the support of labor unions and former president Bill Clinton to turn the race into a close contest heading into Tuesday.

With 94 percent of the precincts reporting, Critz led Altmire 52 percent to 48 percent.

Altmire, who campaigned as someone who knows the district, frequently boasted of his record of perfect voting attendance. Critz, however, ran as the Democrat more true to his party’s core values, with Altmire’s opposition to the 2010 health-care law a key factor in swaying union support to Critz’s side.

Critz, who was not in Congress at the time of the health-care votes, worked for the late congressman John P. Murtha, whose pork-barrel politics were legendary in the region and whose close bond with Clinton helped him snag his endorsement.

Critz must now try to win a district that backed Sen. John McCain (R-Ariz.) by 54 percent in the 2008 presidential election. Republican lawyer Keith Rothfus, who narrowly lost to Altmire by two points in 2010, will square off against Critz in November.

The losses by Altmire and Holden, in the new 17th District, are another blow to the Blue Dog Coalition, a caucus of moderate to conservative Democrats from rural and exurban districts. Once numbering more than 50 members, the Blue Dogs were cut in half by the 2010 GOP landslide and a handful have decided to retire rather than seek reelection.

After nearly 20 years of representing a swing district, Holden found the new district to be a repository for more liberal Democratic voters who were taken from other districts held by Republicans. This exposed Holden to Cartwright, who used his personal wealth in the race, as well as liberal groups and the Campaign for Primary Accountability, an anti-incumbent super PAC. Combined, those forces spent more than $1 million against Holden. Cartwright won, 57 percent to 43 percent, with 99 percent of the votes counted.

Among the House Democrats ousted in November 2010 was Patrick Murphy, a former military lawyer who served the Iraq War and became an opponent of the conflict after winning a suburban Philadelphia seat in 2006. Murphy, 38, a former Blue Dog who opted not to run for his old House seat, lost his bid for the party nomination for state attorney general to prosecutor Kathleen Kane.

If Kane can defeat GOP prosecutor David Freed in the fall, she will have a chance to become a major figure in Pennsylvania politics, providing a leg up on the governor’s nod in future races.

With 87 percent of the vote counted, Kane led Murphy, 53 percent to 47 percent.

Despite the GOP’s major victories there two years ago — picking up the governor’s mansion, a Senate seat and netting five House seats — Pennsylvania Republicans have lost some momentum.

Sen. Robert P. Casey Jr. (D) entered the election cycle last year as potentially vulnerable for his first reelection bid, but recruiting lagged and left a GOP primary field that was somewhat undistinguished. The winner was coal-mine magnate Tom Smith, who has pent more than $5 million of his own money.

With 88 percent reporting, Smith had 41 percent of the vote, more than twice as much as his closest of his four rivals.

Staff writer Aaron Blake contributed to this report.