A month before a suspected white supremacist walked into the Holocaust Memorial Museum in downtown Washington and opened fire, the Department of Homeland Security warned that domestic right-wing extremism was the most pressing domestic terrorist threat that the country faced. [See photos of the scene at the U.S. Holocaust Memorial Museum]

Conservatives were outraged that the DHS analysts had singled out antiabortion and antitax radicals for scrutiny. But the report was part of a series that DHS compiles on domestic dangers from all sides of the political spectrum, an area that's taken a back seat to overseas threats.

A series of recent incidents shows the prescience of those reports and illustrates the worrying reality that terrorism often comes from inside the homeland. Worse still, the reports caution that such attacks are likely to happen again. In the past two weeks, the country has seen the bombing of a Starbucks coffee shop in New York City, the arrest of four men for allegedly plotting to blow up synagogues and shoot down planes, the shooting of two soldiers at an Army recruitment center in Arkansas, the assassination of a doctor inside a Kansas church, and the shooting at the Holocaust Museum. Although these are not all cases of right-wing extremism, each is an example of domestic terrorism. "We still face threats from al Qaeda," FBI chief Robert Mueller warned Congress in May during a briefing on threats facing the nation. "But we must also focus on less well-known terrorist groups, as well as homegrown terrorists."

The man authorities say was the shooter at the Holocaust Museum, James von Brunn, was a well-known white supremacist who had railed against blacks, Jews, and the power of the federal government. In 1981, Brunn walked into the Federal Reserve Board with a shotgun, according to news reports. In another incident in early April, three police officers in Pittsburgh were killed by another reported white supremacist. [Read The Holocaust Museum Shooting and the Right's Image]

In another recent high-profile incident, George Tiller, a Kansas doctor who performed legal abortions, was shot and killed last Sunday as he stood in the aisle of his church. Scott Roeder, the man charged in Tiller's murder, echoes the DHS report on right-wing extremism. Believed to have been a member of an antigovernment militia in Montana during the mid-1990s, Roeder had a history of railing against taxes and abortion, according to news reports. "We can see from these incidents that the U.S. is not immune from these types of attacks and that a lone gunman or cell can kill just as effectively," says Bruce Hoffman, a terrorism expert at Georgetown University. "But it also shows that those operating outside an organized terrorist network lack the training and tradecraft to make their attacks either sustained or a systemic threat." After the killing, the U.S. Marshals Service was instructed to increase security at the country's abortion clinics. [Read A Leading Abortion Foe Reacts to Tiller's Murder]

There was no call to reinforce security at military recruiting stations, however, after Abdulhakim Muhammad allegedly shot two soldiers smoking cigarettes in the parking lot of an Army center in Arkansas. Pvt. William Long was killed and another soldier was wounded. Muhammad was reportedly angry over the wars in Iraq and Afghanistan. On Tuesday, he pleaded not guilty to murder charges.

Four Muslim men also pleaded their innocence before a judge in a White Plains, N.Y., courthouse after being accused of plotting to blow up a pair of synagogues and down military aircraft with a shoulder-fired missile. The feds had been keeping tabs on the men for a year and sold them the missile and explosives, which had been deactivated. The four were reportedly angered over the deaths of Muslims in Afghanistan at the hands of U.S. forces. [Read Five Top Fears (Other Than al Qaeda) of U.S. Spy Agencies]

The motives are less clear for a bizarre bomb attack early last week that hurt no one but blew out the windows of a Manhattan Starbucks. Police speculate that antiglobalization protesters, who've targeted the coffee chain in the past, may have been responsible. While these latest attacks are examples of more traditional violence, DHS is gearing up for yet another new type of threat: cyberattacks.