WASHINGTON — Lawmakers want to know if military and homeland security leaders are doing enough to monitor the armed forces for signs of white nationalism and other dangerous extremism in the wake of the arrest of a Coast Guard lieutenant with radical views who was plotting mass murder.

In a letter to leaders at the Departments of Defense and Homeland Security on Monday, the group of Democratic House members said they want assurances that the recent case is not “indicative of a larger, systemic issue within the United States Armed Services.” They also said they are concerned with reports of other racist activity in the ranks.

“Beyond the extremes of domestic terrorism, we are additionally concerned with low level racism and other identity-based harassment that disrupts unit cohesion, impacts readiness, and degrades the ability of our servicemembers to protect our nation,” the letter said.

“Servicemembers who experience or witness racist or hateful behavior must be able to report such behavior without fear of repercussions.”

Coast Guard Lt. Christopher Hasson was arrested on Feb. 15 on charges of illegal possession of firearms and drugs. But investigators said they also uncovered plans by Hasson to conduct a large-scale, violent attack in the Capital region, developing a list of political and media targets he identified as “traitors” to America.

Hasson previously served in the active-duty Marine Corps and Army National Guard, moving frequently. Investigators have found evidence that he was a long-time white nationalist who held violently racist views even before his first enlistment in the military.

The lawmakers — California Democratic Rep. Jackie Speier and Maryland Democratic Reps. Anthony Brown, Elijah Cummings and Jamie Raskin — said those revelations come on the heels of previous investigations that found at least six active-duty troops or veterans took part in the white supremacist rally in Charlottesville in August 2017.

“The involvement of service members in these activities is cause for significant concern, particularly given their combat and weapons training,” they wrote in the letter, first made public by the Washington Post.

Nearly 1 in 4 troops polled by Military Times in 2017 said they had seen examples of white nationalism among their fellow service members. Among non-white members of the military, the figure was more than 40 percent.

Pentagon officials in recent years have reiterated that extremist views are counter to military ethics and potentially punishable under military law.

But in their letter, lawmakers are asking for proof that those views are being monitored and that recruits with dangerous views about other races or cultures are not being allowed to enlist. They also want to know how Hasson was able to avoid detection for years, amassing an arsenal of weapons and hatred without alerting military authorities.

Analysts from the Center for Strategic and International Studies last November said the rate of far-right extremist attacks has risen steadily in recent years, and poses a greater threat to Americans than attacks from Islamic extremists.