Hillary Clinton emerged recently to claim, with no basis in fact, that I am being “groomed” by the Russian government to undermine America. As a major in the National Guard who served in Iraq—one of the many disastrous regime-change wars Mrs. Clinton championed over her career—I swore an oath to only one authority: the U.S. Constitution.

I’m running for president to undo Mrs. Clinton’s failed legacy. From Iraq to Libya to Syria, her record is replete with foreign-policy catastrophes. It’s a primary reason why I resigned as...