As noted by the Washington Post, the missiles originated from North Korea's west coast and traveled more than 600 miles before splashing into the Sea of Japan. This action coincided with military exercises being conducted by the U.S. and South Korea. Such maneuvers have traditionally been characterized as provocative by North Korea.
In Gardner's view, the missile launch is especially worrisome given assertions by North Korea that it has developed a weapon capable of reaching American soil. Experts have previously expressed doubts that this is true, but in recent months, more of them believe in the possibility — hence Gardner's interest in the Terminal High Altitude Area Defense system, which was created to shoot down a variety of ballistic missiles in what's known as their terminal phase.
In addition, Gardner calls for diplomatic outreach to allies in the region, and while he doesn't mention North Korean leader Kim Jong Un by name, there's no mistaking his reference to the "madman in Pyongyang."
Here's Gardner's full statement:
“North Korea’s reported launch of multiple missiles comes approximately one month after the regime claimed it successfully tested a new type of ballistic missile. Pyongyang’s growing aggression must be met with a tough policy response from the United States, including new sanctions, show-of-force exercises in the region and the expedited deployment of the Terminal High Altitude Area Defense (THAAD) system. It is also important that we strengthen our alliances in the region and reassure our allies South Korea and Japan that the United States unequivocally stands with them against the North Korean threat. I look forward to seeing immediate and determined actions from the Trump Administration and will be asking for a full briefing outlining the actions it will take to stop the madman in Pyongyang."