Compared to where we are today, the founding fathers would be considered libertarian if they were around today. They never believed in standing armies or income tax (directly apportioned tax is directly forbidden in the constituion unless it is returned directly to the people). America of the first 150 years would also be considered libertarian, as would have pretty much all of the political parties' positions compared to today. Even the republicans of only 40 years ago would be considered libertarian by today's standard.

In america's most properous period it was essentially libertarian (compared to today, it's least prosperous period- at least in terms of economy and freedom). The problem is that federal government has been bloated out of recognition to where the only option now for a consitutional government is libertarian. It's hardly a radical idea, it's been around since 1776, but we didn't need a libertarian party until about 50 years ago when the feds started bloated no matter who we voted for.

Contrary to ignorant views, both libertarians and anarchists believe in government. Libertarians believe essentially in the constitutional american government of the founders, and anarchists want to do away with the federal government (and even most state type government) and only have essentially what amounts to county government. There are all shades in between and at the outside, but that's the gist.