Bush wants to be seen as a "war president" (story) and his political team thinks that national security is his best case for re-election, but his handling of the War on Terrorism has been a total disaster.
Of course it is true that there hasn't been a terrorist attack within the borders of the United States since September 11th, 2001. Also, the war against Al Qaeda has resulted in the killing or capture of a large number of top Al Qaeda operatives. The Al Qaeda training bases in Afghanistan were destroyed, putting them on the run. The pro-Al Qaeda Taliban government of Afghanistan was removed. Up to this point Bush had done a good a job as any president could likely have done under the circumstances.
Then it all changed.
Bush's insistence of going to war with Iraq and his attempt to link it with he War on Terrorism was what put us on this downward trajectory that we currently find ourselves in. Bush took all the sympathy and cooperation that the world showed us after 9/11 and flushed it down the toilet. He not only alienated most of the world, but he also alienated most of our allies. Instead of really trying to build a real coalition to carry out his war, he decided to use the "go it alone" strategy.
Bush's test case for the "Bush Doctrine" of pre-emptive war (It would be more accurate to name it the "Wolfowitz Doctrine") has failed miserably. While misguided from the outset, it could have at least been used in a case where our national security was more obviously threatened. Instead, it was used against a state that, while ruled by a brutal dictator, was nicely boxed in after the first Gulf War and the implementation of no-fly zones over a majority of the country. Now that the test case has failed (can you see us even having the ability to invade another country right now, even if we wanted to?), and with the U.S. going to war unilaterally and having stretched our military resources to the breaking point, the next time a real threat presents itself in another country we will find it very difficult to respond. This has put our country in even greater danger than we had been in before the war with Iraq started.