U.S. Rep. Joe Kennedy III (D-Mass.), center left, and Sen. Edward Markey (D-Mass.), center right (R) during a 2017 protest against Trump administration immigration policies. The two lawmakers face each other in a Democratic primary this Tuesday.

Darren McCollester/Getty Images

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Darren McCollester/Getty Images

U.S. Rep. Joe Kennedy III (D-Mass.), center left, and Sen. Edward Markey (D-Mass.), center right (R) during a 2017 protest against Trump administration immigration policies. The two lawmakers face each other in a Democratic primary this Tuesday.

Darren McCollester/Getty Images

Voters in Massachusetts are facing a decision that many wish they didn’t have to make.

For years, now, they’ve been represented in Washington by both the scion of the country’s most famous political dynasty, Rep. Joe Kennedy III, and Sen. Ed Markey, a progressive stalwart who co-sponsored the Green New Deal.

Only one can win another term after Markey and Kennedy square off in a Democratic primary Tuesday.

When Kennedy decided to challenge Markey for his Senate seat, some Democrats in Massachusetts wondered: Why?

“That is exactly how I felt,” said Raul Silva, a 58-year-old civil engineer from Newton, the Boston suburb where Kennedy lives.

Silva has met Kennedy a couple of times and likes him. But he likes Markey, too.

“I think they’re both very effective legislators, and it’s unfortunate that we can’t have both in D.C.,” he said.

In a deep blue state, the winner of the Democratic primary is likely to take the general election in November. Whether the victor is Markey or Kennedy may not make much difference on policy because the candidates agree on most issues.

Voters like Theresa Mattus, a 73-year-old retiree from Millbury, are finding it hard to separate the two.

“I’m, like, 51% Kennedy and 49% Markey,” she said.

Recent polls give the edge to Markey, but it’s been a close race for months.

Large-scale mail-in voting — new in Massachusetts this year because of the novel coronavirus — adds a twist.

Kennedy knows that he or his opponent could make a compelling closing argument, and it might be too late because some voters submitted their ballots weeks ago.

“It’s a wild thing where I’ve got an Election Day that lasts a month,” he said. “Every day you’re going to wake up, and somebody’s going to be casting ballots.”

One way Kennedy has tried to make sure those ballots are for him is to criticize Markey’s record on racial justice. Markey opposed court-ordered busing to desegregate Boston Public Schools in the 1970s and voted for the 1994 federal crime bill that many Democrats now acknowledge has contributed to mass incarceration of minorities.

Kennedy also has the endorsement of the parents of D.J. Henry, a Black college student killed by police in 2010, who say Markey did little to help their family.

“If you truly are a champion for change, if you’re on the right side of social justice issues, act that way when the cameras aren’t on you,” Danroy Henry Sr. said on social media this month.

Markey has apologized for disappointing the Henrys but insists his civil rights record is strong, overall.

And he has fired back at Kennedy, who as an undergrad at Stanford in the early 2000s joined Kappa Alpha, a national fraternity with deeply racist roots.

“He’s changed his position on the racist fraternity — that’s his own words — that he was in for 20 years, and he only left that fraternity one month before this campaign,” Markey said in a recent debate.

Kennedy has said he was previously unaware of the group’s history. But his former membership remains problematic, said Matthew Hughey, a sociologist at the University of Connecticut who has studied fraternities.

“For someone to join KA means, to me, you don’t have a lot of Black friends,” Hughey said. “Because if you had a lot of Black friends, if you had a lot of friends of color, someone would say, ‘Hey, man, do you know about that organization?’ “

Some voters complain that the sniping between Markey and Kennedy — particularly on racial justice — has been frustrating to watch.

Count Daunasia Yancey among them.

“I, personally, am not interested in a pissing contest between these two wealthy white men,” said Yancey, the founder of Black Lives Matter Boston.

Markey didn’t grow up with the privilege of Kennedy, but race and class are two more ways the candidates are similar today.

The contest could be decided, in part, by one of their few big differences: Kennedy is 39. Markey is 74.