From “The Woman King” to Madam President, Viola Davis’ growing roster of fierce commander-in-chief roles reveals a star who takes the words “leading lady” literally, no matter what skepticism audiences may show. The internet seems to have rolled its collective eyes at the idea of Davis in ’90s-style action showcase “G20,” but there’s no actor on earth who could play such a gung-ho U.S. president without some degree of blowback … since there’s no president in U.S. history who’d stand a chance against a G20 summit-disrupting psycho determined to crash the global economy. (Supply your own tariff joke here.)

Clearly reflecting the other candidate in the most recent election, Davis does a fine job of embodying Danielle Sutton, a war hero whose military training and protect-the-little-guy instincts make her an ideal foil for the ruthless Rutledge (Antony Starr). Rutledge has a plan to turn $70 million in...