Two key moments bookended Tuesday night’s U.S. Senate debate between Democratic incumbent Ed Markey and his primary challenger, U.S. Rep. Joe Kennedy III. We probably won’t know for a few days whether either of those moments will matter. But with early voting under way and polls showing the race to be up for grabs, any edge could make a difference.

The first moment came early, when Kennedy brought up recent reports that the parents of Danroy “DJ” Henry Jr. had accused Markey of acting indifferently — even using the term “colored” — at a meeting over the 2010 killing of their son by a white police officer.

“You did nothing,” Kennedy said. “I have stood by that family for year after year through thick and thin.”

Presumably Markey, who has apologized to the Henry family, knew the matter would come up. But he seemed flat-footed, asserting over and over that he, Kennedy and Sen. Elizabeth Warren had all worked together to draft letters demanding an investigation by the U.S. Justice Department.

“When Congressman Kennedy says I did nothing, he knows it’s not true,” Markey said. “He knows it is a falsehood.”

But that merely created an opening for Kennedy, who retorted: “Let’s be very clear. It’s not my words that said you did nothing. It’s Mr. Henry's words that said you did nothing.” Score one round for Kennedy on the crucial issue of racial justice.

The second moment came later. Markey complained that Kennedy’s twin brother, Matthew, is running a Super PAC — a campaign fund not directly affiliated with a candidate — that has been responsible for multiple attack ads against Markey.

Markey then speculated that Kennedy’s father, former congressman Joe Kennedy II, was helping to fund the Super PAC with money from fossil-fuel companies with which he’d done business.

“Is your father funding that Super PAC that is attacking me right now?” asked Markey.

“No clue, no idea,” Kennedy responded. He quickly tried to change the subject, pointing out that it was Markey who declined to sign a “People’s Pledge” keeping undisclosed outside money out of the campaign.

Markey lowered the boom: “I’m sure your father is watching right now. Tell your father right now that you don’t want his money to go into a Super PAC that runs negative ads." As several people pointed out on Twitter, it might have been illegal for Kennedy to do as Markey had demanded, since candidates are forbidden from coordinating with Super PACs. Nevertheless, it was an effective bit of political theater.

And then Kennedy went too far, accusing Markey supporters of pushing social-media posts referencing Lee Harvey Oswald, the man who assassinated John F. Kennedy. Markey seemed genuinely offended at the accusation that toxic internet trolls were somehow tied to his campaign.

““No one affiliated with my campaign would ever say anything like that,” Markey said, dropping his voice. He added that it was “completely unacceptable.”

The debate, broadcast on WBZ-TV (Channel 4) and moderated by political analyst Jon Keller, was freewheeling, although much of it focused on small issues and even smaller differences between the two candidates.

With both candidates espousing progressive agendas, the campaign has come down to Markey’s legislative record, compiled during more than four decades in office, versus Kennedy’s contention that he would lead the fight for the values they share across the country.

“I have more than 500 laws on the books that have been signed by presidents,” Markey said. “That is what I do.”

Responded Kennedy: “The difference is: he’ll vote for it, I’ll fight for it.”

One particularly hot potato Keller dropped in their laps was a question about whether they would endorse a candidate of color next year against Boston Mayor Marty Walsh. It was an opportune moment, Keller said — not only is racial equity an issue that has risen to the top of the national agenda, but Democratic presidential candidate Joe Biden had just chosen U.S. Sen. Kamala Harris, a Black woman, as his running mate. But both men left the tin foil on the spud and tossed it harmlessly away.

“It’s impossible to predict the future. It just is,” Markey said. “You’re asking a hypothetical. Mayor Walsh is doing a good job.” Kennedy added, “Mayor Walsh certainly deserves a chance to make his case.”

The last day of voting (what we used to call primary day) is Tuesday, Sept. 1. Two Republicans are also seeking the Senate seat: Shiva Ayyadurai, a technology entrepreneur, and Kevin O’Connor, a lawyer. The Democratic and Republican nominees will face off to determine the winner on Nov. 3.

WGBH News contributor Dan Kennedy’s blog, Media Nation, is online at dankennedy.net.