Amid a steep rise in health-insurance premiums and persistent concerns over affordability, President Donald Trump has clarified the top priority of his domestic policy chief: the construction of a triumphal arch in Washington, D.C.

While speaking at a White House holiday party, Trump praised Vince Haley—his former speechwriter and a longtime Newt Gingrich aide who now runs the Domestic Policy Council—for his “unbelievable” policy chops, according to a report in the Guardian. Trump then revealed that Haley’s “primary thing” will be overseeing the design and construction of a monument modeled on the Arc de Triomphe in Paris. The structure, he said, would rise near Arlington Bridge, opposite the Lincoln Memorial, and would “blow away” Napoleon’s original.

Haley, according to the president, was moved to near-rapture on first seeing a scale model. “His eyes were teeming,” Trump said. (The Guardian noted that Trump likely meant “beaming.” The project, the president added, would overshadow all other domestic priorities.

That assertion may raise eyebrows among Americans facing sha...