If you're horrified by the thought of a Muslim registry, consider this: It already exists.

On Monday, Dec. 12, hundreds of Muslims and allies took to the streets of Washington, D.C., to take a stand against a possible Muslim registry.

The march, organized by MoveOn.org, Desis Rising Up & Moving, CREDO, and others, saw participants travel from the U.S. Department of Justice to the White House to urge President Obama to take action to prevent his successor, President-elect Donald Trump, from creating a Muslim registry.

"In these moments, before Trump even takes office, it's important to begin building cross-sectional coalitions — especially to protect and defend frontline communities," Iram Ali, campaign director at MoveOn.org writes in an email. "Our march did just that — it brought together a diverse group of organizations to stand with Muslim communities in a time when it's so needed."

It's easy to dismiss the idea that Donald Trump will create a registry for Muslims as farfetched — until you realize that one basically already exists.

In 2002, the newly formed Department of Homeland Security announced the creation of the National Security Entry-Exit Registration System (NSEERS). The program required noncitizens in the U.S. from 25 countries (24 with majority-Muslim populations) to register with DHS. The program created 93,000 cases, but never lead to a single terrorism-related conviction. Finally, in 2011, the Obama administration delisted the countries from the system, effectively ending the NSEERs program.

Ali and others involved in the march want the administration to take things a step further and eliminate the program altogether, writing that shuttering NSEERS "would give Muslim communities a fighting chance under the Trump administration."

But does Trump really want to create a database of Muslims?

In late 2015, Trump said he would "absolutely" require Muslims to register. When asked by an NBC reporter how his plan to register Muslims was different from the registry for Jews in Nazi Germany, he simply replied, "You tell me." He's also called for a ban on Muslims traveling to the U.S. and suggested the government should be surveilling mosques.

Sure, he's walked back some of that language from time to time. And yes, his son Eric recently told a comedian on a transatlantic flight that there wouldn't be a registry. Still, it should be noted that Trump's plan to suspend Muslim travel to the U.S. remains on his website. Even more disturbing, it seems, is what he has in store for the NSEERS program.

Kansas Secretary of State Kris Kobach helped craft NSEERS. He's also a frontrunner to run Trump's DHS.

It was Kobach, along with John Ashcroft, who designed and implemented NSEERS, and thanks to an accidental glimpse from a recent meeting with Trump, it seems like the dormant program will be making a comeback.

In the photo below from Trump and Kobach's Nov. 20 meeting, the document in Kobach's left hand is titled, "Department of Homeland Security. Kobach Strategic Plan for First 365 Days." The first item on the list? Reintroduce NSEERS. Additionally, Kobach has outright said that the new administration is preparing plans for the registry.

Earlier this month, 51 Democratic members of Congress called on President Obama to destroy NSEERS.

In the letter, members of the House highlight some of the big problems with the program and warn of what could happen if it returned. In short, it ravaged communities and instilled distrust.

"When instituted in 2002, the program caused widespread and palpable fear in affected communities, separated families and caused much harm to people affected by it. Boys and men were required to register with local immigration offices, were interrogated, and subjected to serious due process violation. Communities saw family members and neighbors disappear in the middle of the night, held in overcrowded jails and deported without due process. More than 13,000 people were placed in removal proceedings, businesses closed down, and students were forced to leave school with degrees uncompleted."

If President Obama were to rescind the program in its entirety, it would buy civil rights organizations and Congressional opponents of the program some much-needed time to fight back against any efforts by the new administration to start from scratch. It's something he can do before leaving office.

Organizers of Monday's protests delivered petitions totaling more than 341,000 signatures urging the White House to take action.

While the fate of the NSEERS program rests in the Obama administration's hands, there are things that everyday people can do to help our Muslim friends, family, and neighbors.

"Allies can help by taking leadership from Muslims and Muslim communities who have already been impacted by similar policies that Donald Trump is suggesting," Ali suggests. "Many of these policies aren't new for our communities — what is new is the newfound solidarity that we are seeing and that is really important."

She suggests donating to Muslim-led organizations such as Desis Rising Up and Moving and MPower Change.

The coming years will be tough for marginalized groups. That's why it's important for those of us in a position to help stand in solidarity against oppression.

This is something that goes beyond the White House or political parties, but to the core of who we are as people and who we want to be as a country. When oppression exists, where people's rights and expectation of equal treatment are at risk, that's worth fighting for. Today, Muslims are being singled out for disparate treatment; tomorrow, it could be another group.

One thing is clear: People do not belong in a database or a registry like this. Let's take a stand for what is right.