Michigan Democrat Rep. John Conyers Jr.'s Web site features his call for investigations of the U.S. invasion of Iraq and President Bush's authorization of wiretapping without court warrants. Conyers says either could justify Bush's impeachment or censure. It is one of numerous demands by frustrated Democrats, out of power in Congress for several years, for investigations of the Bush administration. But with the growing prospect that they could regain control of at least the House in the November elections, Democratic leaders are signaling that they intend to increase oversight of the White House if they win a majority — and...