After trading bellicose barbs with North Korea throughout 2017, the U.S. heads into 2018 with an increasingly capable foe and no clear diplomatic exit ramps to temper the tensions.
It took decades, but John Coster-Mullen has pieced together specs for America's first nuclear bombs. Some believe his odyssey says something about North Korea's rapid nuclear progress.
Nuclear civil defense fell out of favor in the latter years of the Cold War. But, as North Korea builds its nuclear arsenal, local officials are reluctant to bring it back.
Some lawmakers and experts are raising concerns about the president's unilateral authority to launch nuclear weapons as tensions with North Korea continue to escalate.
"We have lines of communications to Pyongyang," Secretary of State Rex Tillerson said. The State Department later said North Korean officials are not "ready for talks regarding denuclearization."
It is the latest in a tit-for-tat between President Trump and the North Korean leader. In a tweet on Friday, the president said Kim Jong Un "will be tested as never before!"
Senate Foreign Relations Committee Chairman Bob Corker says his committee is considering narrowing the president's ability to launch wars without congressional approval.