When Pete Buttigieg, the mayor of South Bend, Indiana, launched his bid for the Democratic presidential nomination, a key part of his pitch seemed tailor-made to appeal to fellow millennials: "intergenerational justice."

"I think a lot about intergenerational justice," he said in an interview with The Atlantic on Jan. 23, the day he announced his exploratory committee. "Short-term versus long-term helps to explain a lot of the policy disagreements that happen between the parties, and I would argue that in most ways we are the party with more long-term thinking."

As the youngest candidate in the race so far, Buttigieg, 37, defines the concept as more of a governing principle, rather than a set of policy prescriptions.

"To me, it's ensuring that choices made today are responsible and fair — that the distribution of the consequences is viewed not just in terms of how we distribute benefits and costs among people today, but also between people today and people tomorrow," he told NBC News in a recent phone interview.

What intergenerational justice is not, he said, is a conflict among various age groups, noting that he isn't suggesting he can build a movement out of one particular voting bloc.

"One of the most interesting things about what we've seen on the trail so far is that the group I would say is most responsive to this idea of generational change, generational leadership, is actually people my parents' age," he said.

One way Buttigieg suggested it could be put into practice is by having an advocate for future generations in the room when policy decisions are made. Bruce E. Auerbach, an expert on the concept who taught political science at Albright College in Reading, Pennsylvania, said that in Europe, Australia and New Zealand, there have been attempts to promote intergenerational justice through institutional guarantees, while other countries have sought to create an "ombudsman for future generations."

"The great issue, and it's a great issue even in Buttigieg's concept, is that the young are less likely to vote than the old. So, if you're talking about political solutions, there are some barriers," Auerbach said. "If you talk distant generations or even future generations, they have no present voice."

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While Buttigieg has been careful not to offer specific plans, he said, "It's hard to think of a policy issue out there where this isn't at stake."

Here are a handful of issues that Buttigieg has identified as part of his message.

Climate change

Buttigieg said he isn't sure when he first heard the term intergenerational justice, but that he initially began thinking about it "in the context of climate policy as a student learning about how we account for the costs of climate decisions."

"Climate's the classic example" of an issue that should be viewed through the lens of intergenerational justice, he said.

"When those who've been in change before said, 'You know, we shouldn't invest in dealing with this issue,' what they were really saying was, 'We're going to let a future generation pay for this issue.' And the problem is, we are that future generation," he said.

When people ask what I mean by “intergenerational justice,” I mean stuff like this. https://t.co/WLBGL3epTx — Pete Buttigieg (@PeteButtigieg) February 5, 2019

On the campaign trail, Buttigieg has joined several other 2020 candidates in expressing support for Democratic Rep. Alexandria Ocasio-Cortez's Green New Deal, a plan that would eliminate greenhouse gas emissions and put significant government resources into creating a clean energy economy.

Gun control

Buttigieg supports universal background checks and what he described at a Politics and Prose Bookstore event in Washington, D.C., in February as a common sense approach to gun control. He cited his experience as an Afghanistan War veteran to argue that weapons with certain capabilities don't belong on the streets.

"I'm just sick of getting the phone call about a teenager getting shot in my city," Buttigieg told the audience at the event. "Every time I go to one of those vigils, I want it to be the last one. And I don’t think I’ve been to the last one."

At the same time, he said, "I think about how I never want to get a call about that police officer. And I think about all the reasons we don’t want that police officer to be outgunned on the streets of our city."

Can we at least agree on universal background checks? — Pete Buttigieg (@PeteButtigieg) June 16, 2016

Speaking to NBC News, he noted the power of youth activism when it comes to raising awareness around the issue of gun violence.

"Certainly, part of the power of the Parkland students’ movement had to do with their point that a generation of political leaders, you know, including me, that was in charge of this had not successfully kept them safe,” Buttigieg said, referring to students of the Marjory Stoneman Douglas High School in Parkland, Florida, where 17 people were killed in a mass shooting on Feb. 14, 2018. "And I think it’s helped people be more open to undertaking gun safety measures like universal background checks."

Fiscal policy

In an interview with PBS, Buttigieg floated the idea of a financial transactions tax and suggested he would be open to reconsidering the top marginal tax rates.

When it comes evaluating monetary policy through the intergenerational justice lens, he told NBC News that it would mean asking "whether we really think that we would be able to grow ourselves out of the new debt that we take on or whether we’re simply asking a future generation to pay for something we'd like to have.”

He acknowledged that confronting an issue like climate change probably would not be possible without deficit spending.

“But we’ll have to choose to plow that spending into the things most likely to earn a return, so that we’re not simply saddling our future selves or our descendants with costs of what we’re doing today,” he said.