The U.S. air transportation network (ATN) is critical to the mobility and the functioning of the United States. It is thus necessary to ensure that it is well-connected, efficient, and robust. Despite extensive research on its topology, the temporal evolution of the network's robustness and tolerance remains largely unexplored. In the present paper, a temporal study of the domestic U.S. ATN was performed based on annual flight data from 1996 to 2016 and network analytics were used to examine the effects of restructuring that followed the 9/11 events along with the current state of the system. Centrality measures were computed to assess the system's topology and its global robustness. A node deletion method was applied to assess the network's tolerance by simulating a targeted attack scenario. The study showed that the 9/11 terrorist attacks triggered vast restructuring of the network, in terms of efficiency and security. Air traffic expanded, as new airports and air routes were introduced. Airlines reconsidered their strategy and optimized their operations, thus allowing the network to recover rapidly and become even more efficient. Security concerns resulted in significant improvement of the network's robustness. Since 2001, the global traffic and topological properties of the U.S. ATN have displayed continuous growth, due to the network's expansion. On the other hand, the robustness of the system has not shown an improving tendency. Findings suggest that although the system's ability to sustain its operational level under extreme circumstances has lately improved, its tolerance to targeted attacks has deteriorated. The presented methodology may be applied on different network levels or different transportation networks, to provide a general perspective of the system's vulnerabilities.