The situation Abraham Lincoln faced was unique. In his view, the United States was threatened with destruction, ruin, overthrow, perishing - all words that he used - which is not the case for any other president, including the current one - Barack Obama.

Abraham Lincoln had a deep realism; he did not deceive or mislead himself, but faced the world he had to deal with as it really is. At the same time, he had a striking moral intelligence, and a confidence in the working of his own mind and conscience.

There was specific constitutional provision for emergency measures in the case that Abraham Lincoln faced - an insurrection - which no other president has faced.

All presidents - particularly war presidents, presidents inclined to the imperial presidency - invoke Abraham Lincoln as a justification, but they omit these three defenses of Lincoln's strong actions. Suspend habeas, blockade, increase army without congress, arrest Maryland legislators, etc.

After I published a book called Lincoln's Virtues a wit said that my next book should be Lincoln's Vices. But in my opinion that would be a short book!

Abraham Lincoln had great clarity of mind and expression, and he worked to make it clearer -reading Euclid in his early 30s to train his mind.

It is very hard to answer the oft-posed questions about how Abraham Lincoln would respond to some current condition. My favorite story on that count is that the late great Lincoln scholar Don Fehrebacher was asked, during the struggles over bussing for racial balance a few years ago, what Lincoln would say about "bussing" and he thought awhile and then answered : "what Lincoln would say would be: "What's a bus?"