Clinton is scheduled to meet with Republican and Democratic leaders of Congress at 2:30 p.m. ET Tuesday to lobby for congressional approval of the mission. "This is the toughest sales job of his presidency," says White House correspondent James Carney. "But even if he does a reasonable job of offering a rationale for sending American troops to Bosnia, and Congress backs him, the numbers will more than likely be soft. As big a challenge as this is, the bigger challenge will come later, in two and three months, if there are American casualties." For now, the White House is talking tough, promising that U.S. troops will respond to any threat with instant and overwhelming force. Hearings in Congress, which would have to pay for the deployment, are scheduled to begin this week.