PITTSBURGH — Reps. Mark Critz and Jason Altmire debated for the second time in as many days this evening, striving to define their differences ahead of the April 24 Democratic primary.

In an otherwise tepid exchange, Critz emphasized his support from local labor unions, and Altmire underscored his Congressional voting record as reason to keep him in office.

“Every major union that has endorsed, has endorsed me,” Critz, serving his first full term in Congress, declared. “What that tells people is there are groups that know both of us, and they know they can trust me.”

Altmire, meantime, cited the more than 4,600 votes he’s cast in Congress since his 2006 election.

“Most importantly, I work hard. I show up for work. I travel the district. I’ve never missed a vote,” he said.

But for the most part, the tone was congenial between two House Democrats, who were moved into the same southwestern Pennsylvania district when Republicans redrew the Congressional map last year.

Altmire has the upper hand in the primary because he’s represented 66 percent of the redrawn 12th district — a point he emphasized in his on-camera remarks.

“The fact is the majority of the district as it’s been drawn are people I’ve represented,” he said.

The candidates agreed more often than not during the exchange on issues such as bargaining rights for local teachers, developing energy resources in the region and their disagreements with the president’s policies. Even the moderator, WPXI-TV anchorman David Johnson, commented on the “very collegial” debate and encouraged the two Democrats to “duke it out” more often.

Neither Democrat said he’d be willing to ask the president to campaign for him this fall when pressed by the moderator.

“The way I approach it is I’ve got a Congressional district to run,” Critz said. “I run my race.”

“The success or failure for the candidate for Congress is going to be based on the record,” Altmire said.

Both candidates said they would campaign for the winner of the Democratic primary against the likely GOP nominee, attorney Keith Rothfus. It’s a competitive area, and the winner of the Democratic primary will encounter a targeted GOP race this fall.

Critz repeatedly stumbled over his own words, making offhand comments like, “This is much more difficult than talking to an audience” and “I’m learning how to be on TV.” About halfway through the debate, Critz looked off camera to another television screen and said: “My commercial is on TV. Hey, look at that.”