1) What does "the instrument" mean?
2) Does "the body" refer to "the legislative branch"?
3) What does "the latter" refer to?
This is more particularly the case in relation to that part of the instrument which treats of the legislative branch, and not only as regards the exercise of powers claimed under a general clause giving that body the authority to pass all laws necessary to carry into effect the specified powers, but in relation to the latter also. It is, however, consolatory to reflect that 'most' of the instances of alleged departure from the letter or spirit of the Constitution have ultimately received the sanction of a majority of the people. And the fact that many of our statesmen most distinguished for talent and patriotism have been at one time or other of their political career on both sides of each of the most warmly disputed questions forces upon us the inference that the errors, if errors there were, are attributable to the intrinsic difficulty in many instances of ascertaining the intentions of the framers of the Constitution rather than the influence of any sinister or unpatriotic motive.
Inaugural Addresses of the Presidents of the United States
and not only as regards the exercise of powers claimed under a general clause giving that body the authority to pass all laws necessary to carry into effect the specified powers
Do I have to cram up the meaning? It is still a grammatical baffle to me.