When Colin Powell turns off his TV after the final presidential debate, he will have learned everything he is going to learn about the candidates vying to succeed his former boss, George W. Bush. Powell has made it clear that he has been thinking about an endorsement for a long time but wanted to hear more from the candidates before making his choice. It now seems beyond doubt that Colin Powell will endorse Barack Obama and thereby hammer the final nail in the coffin of the Republican campaign to hold onto the White House.