Meet Trump's acting Pentagon chief

Shanahan, who has been the Pentagon’s No. 2 for 18 months, is little known outside the halls of the national security community — and even there his views are not well understood.

A mechanical engineer by training with scant policy background, the public record of his positions is slim compared to Mattis, a retired four-star Marine general.

“Imagine if we drew a Venn diagram of Secretary Mattis and his skills and background and history and overlaid mine with it,” Shanahan told an defense industry group earlier this year. “At the very edge they would touch, and it’s because we’re both from Washington state.”