Finally, the drawn-out battle for the Democratic presidential nomination has ended and the drawn-out battle for the White House can begin. Are John McCain and Barack Obama right for their respective parties? What will be the tone of the upcoming race? Is it time to say good-bye to the Clintons and the Bushes? All week, Megan McArdle of The Atlantic discusses the McCain-Obama horserace with The American Prospect's Ezra Klein.