Democratic presidential candidates challenged President Bush today on his handling of the war on terrorism, questioning the administration's failure to find Osama bin Laden and Saddam Hussein and asserting that Mr. Bush had failed to protect the nation adequately against further terrorist attacks. The candidates, appearing at a labor forum here this morning, repeatedly castigated Mr. Bush, their presumptive opponent in November 2004, for what the White House has portrayed as one of Mr. Bush's chief strengths: his record in battling terrorism abroad and protecting Americans at home. The criticisms came in a week when terrorists killed dozens of people...