WASHINGTON, D.C. — America’s presidential campaign is already well under way. The election is not until November 2016, and very few candidates have formally thrown their hats into the ring, but the competition to promote and develop ideas — both behind closed doors and publicly — is in full swing.

Earlier this month, Citigroup C, -0.20%  took advantage of this formative political moment by seizing an opportunity to score a tactical victory — but one that amounts to a strategic blunder. Using legislative language apparently drafted by Citigroup’s own lobbyists, the firm successfully pressed for the repeal of some of the 2010 Dodd-Frank financial reforms. The provision was then passed after it was attached to a last-minute spending bill, a tactic that ensured little debate in the House of Representatives and none at all in the Senate.

At a stroke, Citigroup executives demonstrated both their continued political clout in…