Fighting terrorism has reached a “new phase” for the United States, President Obama said during his Oval Office address last night.

As we have improved at gathering information on terrorist networks and at foiling their plots, the president said extremists have turned to “less complicated” measures.

Extremists now use mass shootings as a means to achieve their violent ends. The recent San Bernardino, California, attack, which left 14 people dead, is the most recent example — but it is not the only one. In July, Muhammad Youssef Abdulazeez killed four Marines at a recruiting center and a Navy Reserve center in Chattanooga, Tennessee. In 2009, Nidal Hasan killed 13 people and injured 30 others at Fort Hood.

Besides extremist motivations, the perpetrators in all three mass shootings had something in common — all were able to accumulate personal arsenals of semi-automatic weapons and ammunition to carry out these attacks.

Mass shootings are an easy way for extremists to attempt to demoralize the American population because, “No matter how effective law enforcement is … we can’t predict every would-be mass shooter,” Obama said.

While we can snuff out attacks that terrorist networks orchestrate through intelligence gathering and surveillance, individual extremist gunmen are much harder to track. They can have no criminal record, no direct communication with terrorist cells and no outward signs of violence.

If we can’t track the individual extremists, we must then “make it harder for them to kill,” as Obama said.

All Americans, from both sides of the ideological spectrum, have an interest in keeping weapons, like the AR-15 rifles used in San Bernardino, out of the hands of extremists. Such semi-automatic weapons can reload automatically, allowing shooters to take out numerous targets in a relatively short amount of time.

Yet, despite their deadly efficiency, extremists continue to obtain semi-automatic weapons through legal means — Tashfeen Malik and Syed Rizwan Farook, the San Bernardino shooters, bought all their weapons legally, according to CBS News.

If we want to end the cycle of extremist mass shootings, we need to stop them where they start — gun distributors. We must limit the number of weapons allowed per household, we must limit the amount of ammunition one can buy and we must increase background checks and waiting periods for semi-automatic weapons.

All of which, of course, is extremely controversial politically. Such suggestions seem to be an attack on Americans’ Second Amendment right to bear arms — but this is a matter of national security. Sacrificing the ability of some Americans to accumulate personal armories — so to prevent others from being killed — is a necessary, but ultimately small price to pay.

Of course, countries with tough gun control policies also experience terrorist attacks. On Saturday, for instance, the United Kingdom experienced an attack in an east London Tube station. The perpetrator used a knife to stab three Londoners before authorities subdued him. No one was killed, but if the perpetrator had access to a semi-automatic weapon, would that have been the case?

In order to prevent extremists from committing mass violence here in the United States, “We have to work together to address the challenge,” Obama said. But working together requires both parties to first recognize that we need to do a better job at keeping high-powered weapons out of the hands of extremists.

Until we do this, the cycle will continue to repeat itself, and extremism will continue to have its day on American soil.