Nothing in modern US politics comes even close to libertarianism. Libertarianism opposes
all regulation of business unless it is in concert with the non-aggression principle (i.e. don't kill, steal, commit fraud, etc.).
Libertarian thinking on antitrust is that it's unnecessary because there is no such thing as a natural monopoly; monopolies are the result of government regulation. Eliminate the regulations that privilege certain businesses over others, and competition will ensure an efficient market.
In reality what we have in the US is a political class which constantly molds regulation to further benefit the shareholders of big businesses. Sometimes they remove regulations to this end, but much more frequently they create or alter them. There's no philosophical bent behind this at all, it's just the strong using government as a tool to oppress the weak (exactly what libertarianism warns us about).
Nobody has ever pandered to libertarians when trying to justify their policies, so I have no idea why people like to blame them.
To me a sign that the libertarians are on to something is that no government has ever dared to try it. Governments are comprised of powerful people and if they did they would lose all that power...