As a side note: that phrase comes from Oliver Wendell Holmes. What it means is this: we cannot stand idle, just because of the Constiution, if the alternative is defeat or dishonor.

I, of course, recall the example of Lincoln in the Civil War. However, there is another, clearer example.

History agree that Thomas Jefferson was an abject failure as the Governor of Virginia during the Revolutionary War. This is because he adhered to the strict letter of the law, even when it meant passitivity in the face of British moves. His successor, Patrick Henry, did not follow such a legalistic line and, consequently, was much more successful.