In its first 24 hours, Bernie Sanders’s political ad had been viewed almost 1 million times. Our colleague on the Sanders beat described the Democrat’s new 60-second presidential campaign commercial this way:

There are images of Iowa farms, the New Hampshire seacoast, coffee shops, kitchen tables and thousands and thousands of inspired Bernie Sanders supporters, in intimate settings and at the large-scale rallies that have come to define his campaign.

The new 60-second television spot reaches its crescendo as Simon & Garfunkel sing “they’ve all come to look for America” while an expanding grid of people who’ve all come to see Sanders flashes on the screen.

[Bernie Sanders goes ‘hope and change’ in closing ad featuring thousands of inspired supporters]

It’s almost impossible to watch it, regardless of political persuasion or candidate preference, and not feel a familiar tug at your heart. It’s rare for a political ad to evoke such universal emotions. But its power is in its universality. The images of everyday Americans doing everyday things set to a powerful song from perhaps the most unsettled time in our nation’s history taps into one powerful human sentiment: Nostalgia.

At one time, nostalgia was viewed negatively. It’s derived from two Greek words, nostos, meaning home, and algos, meaning pain. It was associated with people longing for the past and feelings of homesickness.

But modern research has found that reflecting on the past can provide more comfort than hurt. Constantine Sedikides, a psychology professor in England who has extensively studied the positive impacts of nostalgia, told the Guardian in 2014 that the mental state was the “perfect internal politician, connecting the past with the present, pointing optimistically to the future” and  “absolutely central to human experience.”

The softness in our hearts for the past explains the popularity of articles and TV segments that list toys or music or phrases from previous decades. It’s why reboots of shows like “Full House”  or new installments of movies like “Star Wars” using the original cast are so exciting. Harkening back to a simpler time, even if it was only simpler in your rose-tinted memory, can actually make us happy.

Sanders’s campaign expertly exposed that vulnerability in all of us. The wordless images set to soaring music allows us to sit with those emotions without being explicitly told what to feel.

The choice of music, Simon and Garfunkel’s “America,” plays an especially integral role in taking viewers to that sentimental place.

A 2013 study from the University of Southampton, where Sedikides teaches, looked at the impact of music to bring about nostalgic feelings. People reported feeling more optimistic when presented with a song that had been identified as nostalgic.

Another study, also co-authored by Sedikides, showed that nostalgia makes people feel socially connected, which is why tapping into it works so well in advertising. Sanders’s ad leans heavily on the themes of togetherness and community.

Susan Holak, dean of the School of Business at the College of Staten Island, who has studied nostalgia, said the ad’s visuals represent family and home, which are common elements in evoking nostalgia.

“Those are universal images,” she said. “There are key recurring themes related to nostalgia and they relate to people and certain collective events.”

A Reddit conversation started Thursday discussed how and why the ad is resonating:

“This is the first ad (from any candidate) that gave me chills in a good way.”

“That has some serious throwback appeal.”

“Those were days when it didn’t cost much to just get on a bus with your SO and just set out to explore. Everybody was trying to ‘find themselves’ as they grew up.”

“I really did get chills and I started to well up. Not being hyperbolic, that was so simple and elegant. No attacks just people. The American people.”

Krystine Batcho, a professor at Le Moyne College, who also studies nostalgia, said the song itself targets baby boomers, and perhaps their children who remember their parents playing similar songs growing up. It’s “personal nostalgia,” she said, which is the most powerful, memorable kind.

But the ad has cross-generational appeal.

“The ad does an excellent job keying into what is most characteristic of nostalgia – social relationships. If you look at the imagery in the ad, it’s highly social. Even when it’s two or three people on the screen, that is all about relationship,” she said. “When people remember back over their lives, their memories are full of people. The moments they recall are not the most extraordinary things. They are the ordinary things. They might remember their grandmother used to help them bake cookies. It’s the coming together of people.”