Civil rights advocates say the arrest of a Coast Guard lieutenant charged with planning a massive domestic terrorist attack show the military has allowed a problem with white nationalism in the ranks to fester while it focused on aggressively vetting immigrants.

Since 2017, branches of the U.S. military have boosted background checks on immigrant recruits, changing the naturalization process, adding extra security screenings and discharging hundreds who had been recruited specifically for valuable foreign language and medical skills.

At the same time, advocates charge that military officials have failed to take effective action to root out enlistees who support white nationalism and white supremacy, pointing to the case of Christopher Paul Hasson, who was arrested last Friday, as a notable example.