"Al Qaeda's affiliates have proven resilient and are positioned to make gains in 2016," Clapper, a retired US Air Force general, said. "Al-Qaeda in [the] Arabian Peninsula and al-Nusra are the two most capable al-Qaeda affiliates."
However, the Islamic State, also known as Daesh, had established a greater capability than al-Qaeda so far to inspire terror attacks within the United States, Clapper cautioned.
"US-based HVEs [homegrown violent extremists] will probably continue to pose the most significant Sunni terrorist threat to the US homeland in 2016," Clapper added.
The July 2015 attack against military facilities in Chattanooga, Tennessee and the December 2015 attack in San Bernardino, California in which 14 people were killed demonstrated the threat that HVEs already posed to the homeland, Clapper said in his testimony.
In 2014, the Federal Bureau of Investigation (FBI) arrested approximately one dozen US-based Daesh supporters. In 2015, that number increased to approximately five dozen arrests, Clapper concluded.