But militias were also about as prominent a couple decades ago, during the Clinton administration. In between, during the second Bush administration? A huge drop.
Consider this data gathered by the Southern Poverty Law Center. Keep in mind that a Democrat occupied the Oval Office between 1996 and 2000 and a Republican from 2001 to 2009. Of course, between 2009 and 2015, the Democrat in the White House has been Barack Obama.
New militia groups were in decline in the last couple years of the Clinton administration, but the biggest year for militia groups since 1996 was actually long before Obama, in 1996 -- right in the middle of Clinton's presidency. Back then there were 370 such groups.
That number dropped to 35 by the middle of the Bush administration, but is now back up to 276.
The Center is an Alabama-based nonprofit which is actively and vociferously loathed in certain conservative circles. However, it is one of the best sources of empirical data and information about extremist political activity in the United States because the discrimination watchdog agency and think tank employs former reporters and editors, investigators, law enforcement and security analysts. These people comb through and compile publicly available data and tips from police, subscribe to group publications and send staff out to events to gather the information needed to generate an annual report about various types of groups and organizations each year. Their data, gathered and reported at regular intervals, also helps to clarify the range of social, political and economic events that may drive group trends.
So what really is behind this not exactly precise pattern? Well, the general growth of militia groups during the last two Democratic administrations and the reduction under a Republican one is driven largely by the principal concerns and fears of the people who join these groups and the way they understand the goals of the respective political parties. Militia and so-called "patriot" group members typically fear greatly or subscribe wholeheartedly to conspiracy theories that indicate that the federal government aims to take all Americans' guns, to put true patriots into camps -- specifically Federal Emergency Management (FEMA) Camps during the Obama years -- socialize or expand state control of different facets of the economy (health care, energy production and profits, etc.) and generally impose tyrannical control. If you think about it, that language crops up, often unchallenged or obstructed by facts, a little more than often on conservative information and commentary sites.