Bulwark of the Republic: A Biography of the Constitution, Burton Hendrick, 1937.
Here's a review from Time magazine the summer the book was published. I don't recall the author being the enthusiast about the usurpations of Roosevelt II that Time presents, but then I haven't read it in a decade - my last reading of it was in '98 or '99 when our second child was a baby. The reading before that was in '89 or '90; I recall reading the sections on Webster and Lincoln at the laundromat in Shelbyville back when I was working at Butch's Amoco in Findlay.
I'll give it another read now that one of our two copies has been discovered on a bookshelf in the foyer.
(Come to think of it, The Founders' Constitution is now my favorite book, with Bulwark probably coming in second. All this is after the absolute frontrunners, Psalms and the Gospel of Mark.)