In late January, Bernie Sanders supporters released a feel-good video that went viral. Democrats really liked it — but perhaps more surprisingly, our new research shows that Republicans kind of liked it too.

This might be because it's an ad that illustrates what we all want to believe about democracy: that together we can make America better.

So we partnered with media and polling company Morning Consult to show 116 voters this ad. As they watched this 30-second spot, we asked them how favorable they felt about the ad, and virtually everyone — Republicans, Democrats, and independents — felt pretty good about it.

Afterward, we asked them how this ad changed their opinion of Sanders.

The way Republicans responded reveals exactly how partisanship colors how people react to an ad, even if they feel good about it. It's a strikingly concise example of America's increasing polarization.

Why we polled this ad

Sanders is among the most left-leaning presidential candidates in recent history, a man who has introduced himself to a national audience by calling himself a "democratic socialist." So it makes sense that liberals can watch this ad and feel emotional as the ad crescendos into a scene of a large crowd cheering for his political revolution. But what about everyone else?

Here's the video and the results:

Republicans felt above average about the ad — but it made them dislike Sanders more than before

The way Republicans responded is nothing short of fascinating.

They felt favorable about the ad the entire way through, which is quite rare for any partisan to feel about a candidate on the other side. And when they were asked about it afterward, they were lukewarm on how credible they felt it was — but said it wasn't terrible. There was, after all, very little content in the ad.

Then they were asked if they had a more or less favorable opinion of Sanders after watching this ad. The most common answer was that they felt less favorable about him, followed by people who felt the same as before the ad. Very few people felt better about him.

In case you missed that: They liked the ad. But it made them dislike the candidate more than before.

Democrats and independents loved it. What does that mean?

Democrats and independent favored this ad and found it credible, which isn't a surprise. And the large majority of them felt more favorable toward Sanders afterward. Since Sanders needs to win the primary with Democrats and independents, this is good news.

But here's the main problem: There is very little evidence that campaign ads make a noticeable difference in an election. They matter more with candidates who aren't as well-known, but otherwise the effect — especially with positive ads — has been tough to detect.

That said, there is evidence that ads do have a short-term effect. They can sway a decent number of voters for about a week after they view it. So the right placement of an ad like this could swing a primary a percentage point or two, but measuring the effect is incredibly difficult.

These rare feel-good ads are what we want to believe about democracy. These poll results show something else happening.

The Sanders ad was elegant, not only in its artistic execution but also in that it weaves together Sanders's core message of income inequality with a nod to racial inequality. Sanders has struggled to win over minority voters, but this video threads the needle in merging these two messages with a hopeful tone that was reminiscent of 2008 Barack Obama ads.

Shortly after the original creators released the video, the Sanders campaign contacted them and made this into an official campaign ad.

No other candidate this election has released an ad like this. And that's because a) the Republicans have been focusing on attack ads, which generally have a larger effect on the polls, and b) not every candidate can pull off this kind of ad.

The tenor and circumstances of this ad are eerily similar to that of the "Yes We Can" Barack Obama video from 2008:

Black Eyed Peas frontman and Obama supporter will.i.am used Obama's concession speech in New Hampshire to construct a song that takes advantage of Obama's repetitive cadences. It is sung over a montage of diverse artists in a recording studio. The ad strikes a hopeful tone, which taps into a very simple narrative: Together we can make progress.

The Sanders video — also created by a supporter — does something similar, in that it takes advantage of the candidate's punctuated rhetoric, which builds and builds over a song that does so too. It strikes a similarly hopeful tone that says, Together we can fight for each other.

Both campaigns had strong enough central messages that they allowed an artist to create an ad like this. It's a simple narrative arc of where we are and where we can go — but only if we do it together. It's the hopeful promise that we all want to believe about democracy.

Our poll numbers show that American voters are together for the duration of this ad. We have similarly positive feelings, which is more than we can say for most political ads.

But that shared sentiment goes away almost instantly afterward — Republicans go one way while Democrats go the other. And a week later, it's likely even Democrats will forget how this ad affected them.

Partisanship in America is on the rise, and now it's become fair game for hatred toward people on the other side. Even after hearing a message we like, a very simple message that we can agree on, we immediately turn around and go back to our separate corners because of who the messenger is.

Are campaign ads actually effective?