Responding to a rough letter from Bob Dole and Newt Gingrich, President Clinton wrote Tuesday: "There will be no peace without America's engagement. If we turn our backs on this responsibility the damage to America's ability to lead, not just in NATO but in pursuit around the world of our interests in peace and prosperity, would be profound." He added: "If the negotiations fail and the war resumes, as it in all probability would, there is a very real risk that it could spread beyond Bosnia, and involve Europe's new democracies as well as our NATO allies." Given the size and cost of the planned commitment, -- about 20,000 U.S. troops and $1.5 billion by Administration estimates -- the President will almost certainly need the GOP leaders' support. "There is no doubt that the agreements are worthless without the American troops," says TIME's James Graff in Dayton. "Clinton has his work cut out for him."