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In the summer of 1798, U.S. President John Adams faced the gravest crisis of his time in office. Hostilities with the revolutionary, expansionist regime in France had been rising since his election, with French privateers seizing American merchant ships off the Atlantic coast. Adams's effort at diplomacy had backfired. The envoys he had sent to France had been met with extortionate and insulting demands; the publication of their dispatches, in what came to be known as the XYZ Affair, had provoked a firestorm of outrage and war fever, the likes of which the young republic had never before known. The public, led by Adams's own Federalist Party, was demanding a declaration of war. Adams himself had stoked those public passions. But now, in the summer, he hesitated between...