evidence: As a political philosopher with a focus on how people try to reason together through political disagreement, I argue that what matters most is not whether a president lies, but when and why he does so. [...] A justification for these lies might be found with reference to practices which – like warfare or politics – necessarily involve conflict and gamesmanship. No one would expect honesty from the enemy side during warfare, and perhaps one should not from opponents in politics either. Some political philosophers have thought that, when politics becomes an adversarial game, politicians might be forgiven when they seek to deceive the other party. President Biden might rely upon this idea, and could note that the Republican Party is less open to bipartisan negotiation than at any time in its history. Even this last justification, however, may not be enough. Lying to one’s political opponents might be permitted in an adversarial context. The lies told by presidents are often addressed to constituents, and such deception seems harder to justify.