The Flint River is pictured in downtown Flint, Mich., on Feb. 4. The city's water problems began when it switched to using the Flint River for its supply in 2014. They were exacerbated by government officials' failure to disclose and stop the leaching of lead and other toxins into the water. Laura McDermott for NPR hide caption

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Shelter dog Rohan takes a break from his scent detection trials to play outside. Rohan is one of several dogs training to detect homemade bombs at the Canine Science Collaboratory at Arizona State University. Jimmy Jenkins/KJZZ hide caption

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A neighborhood where many people have left their homes because of a massive natural-gas leak is seen in the Porter Ranch neighborhood of Los Angeles in December. David McNew/AFP/Getty Images hide caption

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Democratic presidential candidate Hillary Clinton speaks at her first-in-the-nation presidential primary campaign rally on Tuesday in Hooksett, N.H. Matt Rourke/AP hide caption

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