I think you are right on (2 Chron. 7:14 If my people will humble themselves and pray..." and you sound like you are very sound in your Biblical doctrine and it is great to see a pastor who is Biblically sound (because there are many wolves in sheep's clothing).
I do believe that September 11th tragedy is a wake up call from God and I think the Church in Americacan take responsibility in the spirtual decay of this nation.
I am not going to debate you on this country being founded on Christian principles because I believe it was. I know many of the founders were not Christian but this nation has been predominantly Christian in its young history.
Having said that I do believe the reason God has not taken his whole hand off of us is because of the American church's support for missions. (Some 85% of Christian missionaries worldwide originate in the United States. Tens of millions of Christian converts around the world owe their salvation to the faithfulness of American Christians to spread the Gospel.)
I also believe he has not taken his hand off of us because of our support of Israel (even that is starting to waver I am afraid). Since Israel reclaimed nationhood in 1948, America has been (and continues to be) her truest friend and closest ally. Without America's support, Muslim enemies would have drowned Israel in the Mediterranean Sea long ago.
If the American church repents and turns from its wicked ways, I do think we will see revival in this nation but unfortunately I think 9/11 was short lived of people turning to God and it will probably take something for worse (I pray that it doesn't) to wake up the Church in America and its people who have departed from God.