More: According to the joint task force, all National Guard members who come to D.C. have been deputized as special police by the U.S. Marshals Service and issued a firearm, which is rare for a domestic National Guard deployment. Guard troops are not authorized to make arrests, although they can detain someone until arresting officers arrive.

The troops in D.C. are largely performing what are called "presence patrols," walking in small groups around popular areas of the city to act as a deterrent for crime and allow law enforcement to focus on other areas.

But two different studies " including one out this week by the progressive Center for American Progress " have both found that the National Guard presence in D.C. has had little to no effect on violent crime and that the recent drop in crime would have likely happened regardless of the troops.

"These trends have been going on since before the deployment, since before Trump's second inauguration even. It should tell people that actually this is not part of the solution," says Chandler Hall, associate director on the public safety team at CAP and lead researcher of the study.

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As the length of the deployment, as well as the size, increases, so does the cost to taxpayers. With the current summer surge, the cost per day is hovering around $3 million, according to an estimate by the nonpartisan Congressional Budget Office.

Using that number, the Project on Government Oversight, an independent nonpartisan watchdog, estimates the deployment with this new 2029 extension will cost somewhere between $2.5 billion and $3.4 billion in total, depending on how many troops remain in the city.