No doubt 9/11 was the single worst terrorist attack, but to charactarize the Portland event as an isolated issue is seriously misleading.  Here are (non Muslim related) terrorist attacks since 1900:

Sep 1901: Assassination of William McKinley - 1
Oct 1910: Los Angeles Times bombing - 21
Jul 1916: Preparedness Day bombing - 200
May 1917: lynchings of East St. Louis - 165
May 1919: lynchings in 36 cities during "Red Summer" - 2
Apl 1919: "Anarchist bombings" - 38
Sep 1920: Wall Street bombing - 300
May 1921: burning of Black Wall Street - 150
Jan 1923: Massacre of Rosewood - 45
May 1927: Bath School Disaster - 4
Sep 1962: 16th Street Baptist Church Bombing - 1
Aug 1970: Sterling Hall bombing - 169
Apl 1995: Oklahoma City bombing - 2
Jul 1996: Centennial Olympic Park bombing - 5
Sep 2001: anthrax attacks - 17
Oct 2002: Beltway Sniper Attacks - 2
Jul 2008: Knoxville Unitarian Universalist church shooting - 1
May 2009: Assassination of George Tiller - 1