"Libertarianism is thus the combination of liberty (the freedom to live your
life in any peaceful way you choose), responsibility (the prohibition against
the use of force against others, except in defense), and tolerance (honoring and
respecting the peaceful choices of others)."
I don't see anything there that advocates or justifies an externally imposed government, nor anything that a true anarchist ("without Rulers") would object to. This is why I say "anarchism is libertarianism in full-bloom- with all the contradictions stripped away".
Of course, a person could call himself a "libertarian" and hold views that are incompatible with libertarianism. Just as many people who call themselves "anarchists" support the idea of having a Ruler as long as it is "one of their own guys". Consistency is not a strong characteristic in humans.
A person who supports the Libertarian Party is not necessarily a libertarian. It depends on whether they advocate the use of coercion in any case. If they do, then in that area they are not libertarian. You can not "tax" without coercion. You can not "secure borders" that are along property that is not your own, or along a person's property on whose behalf (without his consent) you are working, without coercion. You can not send "troops" around the world coercing "foreign" individuals to accept Rulers they do not want or to live under a government not of their choosing without violating the core principles of libertarianism. You can not order people how to live, no matter how badly their personal lives offend you, as long as they are not attacking, defrauding, or stealing from an innocent person, and still be libertarian.
A person who venerates the US Constitution is a "Constitutionalist", not a libertarian. Where the Constitution violates the basic human rights of anyone, anywhere, it is wrong. Where it "authorizes" government to use coercion to attain its goals, it is not "libertarian". This is not to say there is no libertarianism in the Constitution; there is just too much other stuff there smothering any libertarianism there might have been.
Look at your "libertarianism" closely before you advocate your non-libertarian views as "real libertarianism". What I write could violate libertarianism somewhere. If it does, call me on it. But, once we examine the disagreement, the position that advocates any form of initiated force/coercion is the position that is not "libertarian", "right" or not.