Bush sounded an optimistic note, promoting himself as the candidate of “Today and Tomorrow,” his campaign’s new slogan. But the baggage of his brother and father seemed to weigh on him. “Our country is on a very bad course,” he said. “The question for me is: What am I going to do about it? And I have decided. I am a candidate for president of the United States.” Amid cheers and off-script, he exhaled with an audible “whoo” that communicated grim resignation, a Here we go.