National Guard troops had become a fixture in DC. Then two were shot.

“The thing I’ll miss most from home is my mom’s stuffing, it’s my favorite," said Clayton Stock-Friends, a young member of the West Virginia National Guard from Harpers Ferry, sporting a red beret and sunglasses. The video messages posted by the Pentagon were filmed outside the D.C. Armory, a building that has become the main staging ground for troops from eight states who have been deployed to the city since August.

On Wednesday afternoon, members of the West Virginia National Guard were patrolling a busy intersection outside a Washington, D.C., subway station when a suspect came around the corner and shot two of them, according to local police. Sidewalks frequented by federal workers, lobbyists, journalists, and nonprofit workers became a chaotic crime scene. A bus stop’s glass was shattered, and Secret Service officers quickly huddled over one victim.

As emergency vehicles swarmed the area, the White House, a few blocks from where the attack took place, and several embassies in the area went into lockdown, and busy holiday flights from Washington’s Reagan National Airport were briefly halted.

The violent attack the day before Thanksgiving, as office workers rushed to airports and the train station with suitcases in tow, shocked a city that had become used to the presence of uniformed soldiers patrolling metro stations and restaurant districts. National Guard members had become a routine fixture in the nation’s capital since they were deployed in mid-August to crack down on what Trump called “rampant crime, murder and death."

As of Wednesday evening, the two unidentified victims remained in critical condition. Law enforcement sources identified the suspected shooter as Rahmanullah Lakanwal, a 29-year-old Afghan national, and said he was in the hospital in police custody.

Aiyana Eirene, a 30-year-old regional manager for a spa company, was in a Lyft heading to a meeting at her company’s Dupont Circle location when she heard shots ring out. She and a colleague had the windows down to enjoy the unseasonably warm afternoon when she said she heard four clear shots, followed by a brief lull and then several more.

“You could feel them, I could hear them perfectly. And then it was just silence, and we got the hell out of dodge," she said.

President Trump vowed that the shooter, whom he called an “animal," would “pay a very steep price." Defense Secretary Pete Hegseth said the Trump administration would be deploying 500 more National Guard troops to the capital, saying the shooting would “only stiffen our resolve to ensure that we make Washington DC safe and beautiful."

The two victims were part of almost 2,200 National Guard members deployed to Washington under Trump’s declaration of a “crime emergency" there. This included 1,300 troops from other states whose governors volunteered them, including Mississippi, Georgia, Alabama, Ohio, Louisiana and South Carolina, in addition to West Virginia.

A week before the shooting, West Virginia Gov. Patrick Morrisey had extended the deployment of roughly 180 West Virginia National Guard members to Dec. 31. When he first deployed his state’s National Guard to Washington in mid-August, Morrisey said he was “proud to stand with President Trump in his effort to restore pride and beauty to our nation’s capital."

The American Civil Liberties Union of West Virginia and the West Virginia Citizen Action Group moved to block the deployment by suing the state, saying that Morrisey had exceeded his constitutional authority by ordering troops to Washington in the absence of any qualifying emergency.

While the presence of National Guard troops in D.C. was initially controversial, residents had grown accustomed to seeing uniformed troops on their commute or at dinner. Visitors snapped photos with them at Union Station or the National Mall. Troops were largely stationed around the city’s downtown area, upscale corridors, metro stations, and tourist hubs.

The National Guard troops almost always worked in groups of two or more, often standing on street corners or walking together, letting pedestrians go about their days.

The deployment of National Guard troops coincided with a surge of federal agents who ramped up immigration enforcement efforts in the city. While masked federal agents were met with protests and jeers, residents who were uneasy about the deployment of military personnel in their city generally kept their distance. Some guard members were occasionally harassed by locals, who in at least one incident shouted, “Traitors go home!"

National Guard members, who are barred by law from engaging in law enforcement, were meant to serve as a visible deterrent, according to Defense Department officials. In recent months they have provided medical assistance, picked up trash, spread mulch, painted fences, and helped elderly locals who fell off their bicycles, according to National Guard officials.

Brian Schwalb, the D.C. attorney general, sued over the deployment and won a court ruling last week in which a federal judge found that the presence of the Guard violated several laws.

The attorney general’s office said in a court filing made a month before the shooting that it had obtained documents suggesting that from the outset of the deployment, officials had worried it “presents an opportunity for criminal, violent extremists, issue motivated groups and lone actors to advance their interests."

By late August, officials had concerns about “a heightened threat environment" for National Guard troops in the capital. D.C.’s local police had also increased patrols in the areas where troops were staying and at times provided police escorts for them, the attorney general’s office told the court.

In a social-media post after the shooting, Schwalb described Wednesday as “a heartbreaking day for DC and our nation."

Write to Vera Bergengruen at vera.bergengruen@wsj.com, Mariah Timms at mariah.timms@wsj.com and Louise Radnofsky at louise.radnofsky@wsj.com