Of course both the Democrats and Republicans in Congress have enabled him and deserve much of the responsibility for his failures, and as a result the U.S. is in for a very, very rough future.
Let's take a look at a few of his biggest mistakes:
1. The election of George W. Bush was as slim as slim gets and a reasonable man would have governed with some humility but instead he tried to use his slim margin to ram home his agenda which of course failed but did succeed in enraging the American left.
2. Post 9/11 management included bureaucratic nightmares such as the Department of Homeland security, affronts to liberty such as the patriot act, and an ill-conceived and undeclared war with ambiguous goals against an amorphous enemy.
3. The medicare prescription drug plan which was designed solely to ensure reelection and has since predictably proven to be anti-competition, wildly expensive, and a subsidy to the pharmaceutical companies that simply insured prices would continue to rise.
4. The Iraq war. This was a poorly managed, poorly planned, undeclared, ill-conceived, unnecessary, and wildly expensive war. Congress has supported this farce of foreign policy every step of the way illustrating not only their complicity in this nonsense but their cynicism and duplicity (in immediately condemning it and doing nothing to fix or stop it) as well. The consequence of this has been to completely ruin our international reputation, weaken our already shaky economic situation, and potentially radicalize another generation of muslims.
5. Nearly doubling the national debt in just over eight years. The potential effects of which include a downgrading of the U.S. credit rating and the potential for massive inflation.
6. The mortgage crisis and the bailouts. This has been in the works mostly since Clinton, who bears much of the responsibility due his changes to the community reinvestment act, but it was the bailouts that truly made this a disaster. Our inept Congress gave away its constitutional obligation of financial oversight and allowed the treasury department unlimited, and unaccountable financial authority which it used to the tune of nearly a trillion dollars in bailouts thus effectively nationalizing our entire mortgage industry. The inevitable consequence of this is likely catastrophe... Why Congress would continue to give more and more power to someone who has shown such utter incompetence in using it shows quite clearly that they are simply biding their time until they can wield that same power - they care little for the success, security, freedom, or happiness of the American people when compared to wielding more and more power.
George W. Bush has not only destroyed the Republican party, of which McCain is its death throes, but he may have entrenched authoritarianism, imperialism, and socialism forever as natural elements of America's modern political and cultural identity. The U.S. is no longer a nation of reason, capitalism, and liberty. It is no longer the political expression of the philosophical enlightenment. It is no longer unique. It is no longer exceptional. It is no longer great.
Our demise has been in the works since Wilson involved us in World War 1 but we have had numerous opportunities to right the ship, but not anymore. The life narrative of the United States of America has run its course and its original brilliance and potential have degraded into a shameful and irrational tragedy.