Nothing gives a sitting president more political capital than fighting a successful war. The thing to remember is that the American people like their wars like an episode of CSI. Neat and tidy and wrapped up in about an hour.
This is the Cheney doctrine. He developed it under Reagan.
According to [Mickey] Herskowitz, George W. Bush's beliefs on Iraq were based in part on a notion dating back to the Reagan White House - ascribed in part to now-vice president Dick Cheney, Chairman of the House Republican Policy Committee under Reagan. "Start a small war. Pick a country where there is justification you can jump on, go ahead and invade."
Bush's circle of pre-election advisers had a fixation on the political capital that British Prime Minister Margaret Thatcher collected from the Falklands War. Said Herskowitz: "They were just absolutely blown away, just enthralled by the scenes of the troops coming back, of the boats, people throwing flowers at [Thatcher] and her getting these standing ovations in Parliament and making these magnificent speeches."
Republicans, Herskowitz said, felt that Jimmy Carter's political downfall could be attributed largely to his failure to wage a war. He noted that President Reagan and President Bush's father himself had (besides the narrowly-focused Gulf War I) successfully waged limited wars against tiny opponents - Grenada and Panama - and gained politically. But there were successful small wars, and then there were quagmires, and apparently George H.W. Bush and his son did not see eye to eye.
Our war in Afghanistan may look on the surface to be just that, but it failed in two major ways. First, there just wasn’t any cool video of things going boom. Americans want this video; they need this video if your war is going to be a success. The Shock and Awe part of the Iraq War was to shock and awe you, not the Iraqi army. Secondly, nobody important got perp walked. Sadly, no one probably ever will. Musharraf would be an idiot to turn Osama over to us.
So, Bush had to find an easy country to topple with little justification. There also had to be a bad guy we could physically get a hold of to perp walk. Hey there is Iraq, they have been under sanctions for a decade and we can easily fool the American people into believing Saddam was behind 9/11. Unfortunately, the Iraq war is now becoming the quagmire that you need to stay out of despite the fact that Bush got his quick initial victory and his perp walk.
This is the reason Bush started talking about political capital after gaining reelection. He believes the Cheney Doctrine, along with gains in the Senate, has given him the God given right to destroy the New Deal.