CINCINNATI, July 22 - In the Second Congressional District of Ohio, which Republicans have controlled for the last two decades, the quickest route to political oblivion could be the one chosen by Paul L. Hackett: calling President Bush a "chicken hawk" for not serving in Vietnam and harshly criticizing the decision to invade Iraq. But Mr. Hackett, the Democratic candidate in the Aug. 2 special Congressional election, is not an ordinary politician. Until four months ago, he was serving in the Marines, commanding a civil affairs unit in Iraq. If Mr. Hackett is elected, he will become the first member...