WASHINGTON, April 12 — As Bill Clinton seeks to finish his memoirs, leading Democrats are voicing concern that the book could overshadow Senator John Kerry's presidential campaign, diverting attention to Mr. Clinton's outsize legacy of scandal and achievement. Many Democrats said they wanted the book published as far as possible before the election and, certainly, before the Democratic National Convention in late July. They fear that the book will embolden Mr. Clinton's foes to turn out and vote for President Bush. Mr. Clinton, for his part, has increased the nervous speculation about the book in Democratic circles by making a...