ALLENTOWN — The empty podium at stage right took a lot of hits on Sunday.

From the opening moments of Pennsylvania’s first Democratic Senate debate, U.S. Rep. Conor Lamb and State Rep. Malcolm Kenyatta lobbed attacks at their missing primary opponent: the front-runner, Lt. Gov. John Fetterman.

In 90 minutes of jabs and jokes, both men — especially Lamb — argued that Fetterman’s decision to skip the debate was an insult to voters and a red flag for his candidacy in a critical Senate contest.

“He didn’t respect you enough to show up today,” Lamb told a crowd of about 175 people at Muhlenberg College.

And Lamb immediately brought up a 2013 incident that has loomed over Fetterman’s campaign, in which Fetterman pulled a shotgun on a Black jogger who he had wrongly suspected of a shooting.

“It was wrong when he did that,” Lamb said in his opening remarks, after telegraphing the attack in the days before. “And he skipped the debate today because he doesn’t think he has to answer. Given everything that’s gone on in this country, that is fatal to his campaign. You deserve a senator that you can trust to show up and not to act like a loose cannon.”

The first debate came just over six week before the May 17 primary, with Fetterman maintaining the substantial lead that he’s enjoyed throughout the campaign as the best-known and best-funded candidate.

And Sunday’s pile-on was expected. With little time left to erode Fetterman’s advantage, the tone of his rivals and the intensity of the race has shifted considerably.

Fetterman, after meeting with supporters at an inn in rural Chambersburg at the same time his opponents were lobbing attacks onstage, called Lamb desperate.

“Conor is in the middle of a meltdown because he saw his poll numbers at 10%,” Fetterman said in an interview, referring to a survey released last week. “So he is resorting to these desperate smears against fellow Democrats that I wouldn’t choose to make, but that’s the campaign he’s running.”

» READ MORE: Conor Lamb’s challenge: Build his name. Take down Fetterman. And do it all with less money.

Fetterman has committed to three televised debates in late April and early May. He said he chose to participate in those debates because they’ll have wider reach. Sunday’s was broadcast on the Pennsylvania Cable Network, while the other debates are set for primetime airing on network TV.

Kenyatta, the only Black candidate in the primary, also went after Fetterman for the jogger incident — specifically his unwillingness to apologize.

“John had nine years... to not just apologize for taking an illegally loaded shotgun, chasing down the first person he saw... but to understand why that was so dangerous,” Kenyatta said. “To understand how that situation could have gone a completely different way.”

Kenyatta said incidents of vigilante justice have resulted in tragedy in recent years, and dismissed Fetterman’s frequent defense that he didn’t know the race of the jogger as irrelevant.

“So often, as we’ve discussed this issue, it’s all come down to whether or not John knew the jogger was Black,” Kenyatta said, “It doesn’t matter the color of skin of the jogger’s skin. One doesn’t have to be racist to be wrong. He was dead wrong. And now he refuses to come here but expects you to vote for him.”

Fetterman defended his actions on Sunday, as he has long done. He didn’t apologize, saying he made a split-second decision to act, as Braddock’s then-mayor and chief law enforcement officer, to what he called an “active shooter situation.” But he said he wouldn’t want to repeat the incident.

Fetterman has long said he heard gunshots not far from his home, saw someone running in the area, called police, and then pursued the man himself to stop him from fleeing. An officer who responded to reports of gunfire searched the man and found he was unarmed, according to a 2013 police report.

“It absolutely was a situation that was chaotic and spontaneous,” Fetterman said Sunday. “And I certainly would never want to repeat it.”

» READ MORE: Conor Lamb says John Fetterman’s afraid to debate, calling shotgun incident ‘a huge problem’

The focus on Fetterman, who was represented by an empty podium on stage, overshadowed a debate that was at times substantive and nuanced, on issues including natural gas drilling. But the candidates themselves kept the focus on that empty podium, in ways big and small.

Lamb, in particular, seized every chance to move the conversation back to Fetterman. Asked about cybersecurity, he criticized Fetterman’s temperament, saying Democrats needed “stable, sensible leadership… Those are some of the traits I don’t believe John Fetterman exhibits on a daily basis.”

A question about the federal debt limit was answered with a criticism of Fetterman’s openness to supporting Medicare for All — and how it would play in a general election against Republicans determined to hold the seat being vacated by retiring Sen. Pat Toomey.

“It’s another $30 trillion... and it scares people,” Lamb said of the program’s price tag. “That’s why the ‘socialist’ label sticks on John. That’s why that punch is going to land.”

The tone between Lamb and Kenyatta was largely cordial, though they did clash at times. Kenyatta called Lamb’s voting record in Congress too conservative.

“You voted for things that are completely out of the mainstream of where Democrats are. And you’ve cut a very conservative record in Congress,” he said, referring to Lamb’s vote to fund former President Donald Trump’s border wall.

Lamb said Kenyatta was misrepresenting his record and that he supported some of the same border security policies as former President Barack Obama.

“For such a passionate Democrat, you campaign just like the Republicans,” Lamb shot back.

» READ MORE: Where the Pennsylvania Democratic Senate candidates do and don’t agree

The biggest policy difference was on hydraulic fracturing, or fracking. Kenyatta supports a moratorium on new natural gas drilling sites. Lamb does not. Even there, though, they both turned the spotlight on Fetterman, who they accused of having shifting positions. Fetterman has said he opposes any bans on new drilling wells, though he has made anti-fracking comments in the past.

Fetterman said Sunday that his past support for a fracking moratorium was tied to calls for more environmental regulations that have since been met. He said that while he wants to fight climate change, Democrats have to “honor and take care of” workers and communities that depend on the energy industry, and acknowledge the national security implications of having domestic energy supplies.

Kenyatta and Lamb agreed on several other issues, including support for making Washington, D.C., a state.

One of their main disagreements was about who can best win a seat that both parties see as critical to the wider campaign for Senate control. Such “electability” debates have come to define the primary contest.

Kenyatta said a working-class candidate like him who understands working-class concerns can excite voters.

“I know that there are a lot of pundits who say Pennsylvania is just not ready to elect an openly gay Black man from North Philadelphia,” Kenyatta said. “But what those pundits never count on is you. Pennsylvania is more ready than the cynics believe.”

» READ MORE: Malcolm Kenyatta is tired of being told he can't win

Lamb noted that he’s won in conservative-leaning districts.

“I have had the experience of going out and being in rooms exactly like this one when there’s not another partisan Democrat,” he said. “I wouldn’t be here with you today if I didn’t figure out how to bring some of them into our camp. That’s what it takes to win statewide in Pennsylvania.”

Fetterman’s absence had at least some impact on voters in the audience.

Beverly Rickles, a retired Allentown school teacher, entered the auditorium with a Fetterman sticker on the back of her phone and the intention to support him. After the debate, she used the phone to take a picture with Lamb.

“They were both able to articulate that Fetterman will not be electable,” said Rickles, who now thinks she will back Lamb.

Jan Beatty, an Allentown city commissioner, said she also came in leaning toward Fetterman. But 90 minutes of attacks against the front-runner had her reconsidering. She was impressed with Kenyatta.

Two hours southwest in Franklin County, Fetterman wore gray gym shorts and a maroon Carhartt hoodie as he talked to about 100 supporters. He said he doesn’t expect to flip the county, which is deeply conservative, but that rural voters are still important.

“We cannot afford to cede any county,” Fetterman said, “any region, any part of Pennsylvania.”