The standing military is actually the last in line to defend the constitution. First and foremost are the people themselves formed as militia. BUT, these days the "m" word has been demonized as the enemy of the state, through state sponsored domestic terrorism! Strong words but none the less true. Sedition, conspiracy, seditious conspiracy, and the use of public funds to deny the power of the constitution of the United States of America or the constitutions of the several states is insurrection! See: http://www.coin-army-usa.org for more on this hot topic.
Further, contained in the web cited above is a letter to the Sheriff Of Palm Beach County touching on the issue of honoring his oath he pleged to the people when taking office!
It is a good read, though many in a complacent stuper will think otherwise!