The time the Clinton campaign accidentally released a Sanders attack ad

Vermont Sen. Bernie Sanders is finally set to appear at a campaign rally with presumptive Democratic presidential nominee Hillary Clinton on Tuesday. It's supposed to be a moment of unity, when the two candidates come together after a long, tough primary season.

On Monday, the Clinton and Sanders campaigns both released a carefully worded statement officially announcing the New Hampshire event. The Clinton campaign also appeared to release something else: an anti-Sanders attack ad.

Finally, Clinton and Sanders enter a political marriage. Will it work?

"The Export-Import Bank," a 28-second spot, was posted to one of the campaign's YouTube accounts Monday afternoon. The aforementioned bank, a government agency that helps foreign buyers purchase U.S. goods, has "supported more than a million jobs nationwide," says the ad, which goes on to list a few of the bank's political supporters, including President Obama (very popular among Democratic primary voters), Joe Biden (likewise), Hillary Clinton (their candidate), Sen. Elizabeth Warren (hey, Sanders fans like her!), Ohio Sen. Sherrod Brown and Franklin Delano Roosevelt, the president responsible for the most enduring social welfare programs in our nation's history.

"This should be a no-brainer," Obama says matter-of-factly in a clip included in the spot.

Then comes a carefully-curated list of the bank's detractors: Ted Cruz, Marco Rubio, the Koch brothers and...you guessed it, Bernie Sanders.

"I urge a 'no' vote," Sanders is shown saying in grainy old C-SPAN footage. Ted Cruz quickly chimes in to agree. It's the kind of "us-vs-them" ad that might have helped the Clinton campaign during the tight primary contest this spring. Two weeks before the Democratic convention, it's just the opposite.

The ad was only up for a few minutes before being removed by the campaign. So how and why did it appear?

A source inside the Clinton campaign, speaking on the condition of anonymity because he was not authorized to speak about the video publicly, said the campaign uploaded the video to YouTube on March 6, when the two candidates were still in the midst of the Democratic primary season. The source also said that the Clinton campaign didn't publish the video, and is looking into how it appeared on the site.

YouTube's console does allow users to upload videos into its system without publishing them publicly.

Clinton and Sanders are scheduled to take the stage tomorrow morning in Portsmouth, N.H.