Seeing that they hate America and want to attack its citizens, the chances are that they will (if not already) make their move at some point.
HOW AND WHY ISIS WILL USE TEXAS TO ENTER THE US IF THEY CHOOSE TO CROSS THE BORDER
Despite tough rhetoric from national and Texas leaders, the vast majority of the U.S.-Mexico border remains unsecured. Areas with frighteningly insufficient security are of particular concern in the state of Texas, largely due to differences in the nature between the transnational criminal organizations that control Mexico immediately south of Texas and the organizations that control the border in New Mexico, Arizona, and California.
To be specific, foreign terrorists would likely enter the U.S. through Texas because the behavior of the transnational criminal groups we more commonly call the Gulf cartel and the Zetas cartel routinely indicate that they are more interested in short-term gains and profit-making than long-term profit sustainability, unlike the various other transnational criminal groups that align themselves under the banner of the Sinaloa Federation. A willingness to accept a large sum of money from a terrorist or group, regardless of the fact that it would lead to a temporary shutdown of the U.S.-Mexico border in the area where the illegal crossing occurred, would be necessary on the part of a specific cartel in order for them to allow such a crossing — and crossings rarely occur unless a cartel allows it.
Understanding the differences between cartels
The Gulf cartel generally controls the Texas border from the Gulf of Mexico to somewhere around the city of Zapata, Texas — roughly the entire Rio Grande Valley Sector. The Zetas control from that point through the Laredo Sector. They are also known to operate well into the El Paso Sector, stopping their activities somewhere prior to the Mexican border city of Juarez, immediately south of El Paso, Texas. This region begins the influence of the Carrillo Fuentes cartel, more commonly referred to as the Juarez cartel. This cartel is aligned with the Beltran-Leyva cartel. Though the Beltran-Leyva shares familial relationships with groups in the Sinaloa Federation, they are currently aligned with the Zetas. The Zetas are in a calm conflict with the overall Gulf cartel, yet they have alliances and working relationships with some groups within the Gulf cartel.