In article ,
says...

When I was commissioned, I swore to defend the Constitution against
all enemies, foreign or domestic. Apparently the U.S. Senate
doesn't have the same requirement.

It is pretty damy close.

http://www.senate.gov/artandhistory/...ng/Oath_Office.
htm

I do solemnly swear (or affirm) that I will support and defend the
Constitution of the United States against all enemies, foreign and
domestic; that I will bear true faith and allegiance to the same; that I
take this obligation freely, without any mental reservation or purpose
of evasion; and that I will well and faithfully discharge the duties of
the office on which I am about to enter: So help me God.

http://clerk.house.gov/member_info/memberfaq.aspx

"I, (name of Member), do solemnly swear (or affirm) that I will support
and defend the Constitution of the United States against all enemies,
foreign and domestic; that I will bear true faith and allegiance to the
same; that I take this obligation freely, without any mental reservation
or purpose of evasion; and that I will well and faithfully discharge the
duties of the office on which I am about to enter. So help me God."

http://www.usmm.org/oath.html

U. S. Maritime Service Oath of Office

Oath for commissioned officers:

Having been appointed an Ensign in the United States Maritime
Service,
I do solemnly swear (or affirm)
That I will support and defend the Constitution of the United
States
Against all enemies, foreign and domestic;
That I will bear true faith and allegiance to the same;
That I take this obligation freely,
Without any mental reservation or purpose of evasion;
And that I will well and faithfully discharge the duties of the
office
On which I am about to enter;
So help me God.

United States Armed Services Oath

Enlistment oath:

I, _____, do solemnly swear (or affirm) that I will support and
defend the Constitution of the United States against all enemies,
foreign and domestic; that I will bear true faith and allegiance to the
same; and that I will obey the orders of the President of the United
States and the orders of the officers appointed over me, according to
regulations and the Uniform Code of Military Justice. So help me God.
(Title 10, US Code; Act of 5 May 1960 replacing the wording first
adopted in 1789, with amendment effective 5 October 1962).

Oath for commissioned officers:

I, _____ , having been appointed an officer in the Army of the
United States, as indicated above in the grade of _____ do solemnly
swear (or affirm) that I will support and defend the Constitution of the
United States against all enemies, foreign or domestic, that I will bear
true faith and allegiance to the same; that I take this obligation
freely, without any mental reservations or purpose of evasion; and that
I will well and faithfully discharge the duties of the office upon which
I am about to enter; So help me God. (DA Form 71, 1 August 1959, for
officers.)