Mengden signed a minor-league contract with the Nationals on Sunday, Robert Murray of FanSided.com reports.
Mengden began the season on a minor-league deal with the Royals, and he posted a 7.36 ERA and 1.90 WHIP in 14.2 innings over six appearances (three starts) at Triple-A Omaha before being released in late June. However, the 30-year-old was able to land a new contract a few days later.