The Obama administration’s crackdown on leaks to the press has snared a high-profile conviction of an FBI linguist, who was sentenced to 20 months in prison Monday after pleading guilty to giving classified information to a blogger. The sentence for Shamai Leibowitz is likely to become the longest ever served by a government employee accused of passing national security secrets to a member of the media. His case represents only the third known conviction in U.S. history for a government official or contractor providing classified information to the press. And it reflects a surprising development: President Barack Obama’s Justice Department...