The first thing to understand is that Hamas is the armed Palestinian wing of the Muslim Brotherhood. The Muslim Brotherhood is an international Islamist network in which national branches are loyal to the main Shura council. Historically, when Muslim Brothers (including Hamas members) change countries, they became members of the Muslim Brotherhood chapter in the country where they reside but typically also continue to work on behalf of their home country causes abroad.
In the 1980s, Muslim Brotherhood leadership commanded every chapter to create “Palestine Committees” to support jihad against Israel and to make up the support network for Hamas. Some of these organizations remain active today, while others have changed names and identities but remain filled with individuals affiliated with the Palestine Committee.
This means the Hamas network in the United States does not consist primarily of “sleeper cells” of terrorist agents who were smuggled across the border. Rather, it is made up of “U.S. persons” — green-card holders, naturalized U.S. citizens, and even second and third generations of U.S.-born citizens who were raised and trained in Muslim Brotherhood-run mosques and who have participated in Muslim Brotherhood organizations.