The Presidential Oath of Office and Section Three

One question about Section Three concerns the President's oath of office. He takes an oath "to preserve, protect, and defend" the Constitution. But Section Three refers to an oath "to support" the Constitution. Is that a meaningful difference? Does the President not take an oath "to support" the Constitution?

Here is what John Norton Pomeroy's well-respected constitutional law treatise said about this in 1868: 

"The senators and representatives, the members of state legislatures, and all executive and judicial officers of the states and of the nation, are also required to take an oath to support the Constitution. The President's oath is but an amplification of this; it enters into more detail, but does not add another compulsive clause. The solemn promise in particulars 'to preserve, protect and defend the Constitution,' does not imply more than the equally solemn promise in generals 'to support' it."