An SPLC recent report said that “nativist extremist’’ groups like Ready’s decreased by almost half in 2011 to 184 groups, down from a high of 319 such groups in 2010.

The Minuteman Project and other similar groups have been plagued by infighting and financial difficulties, largely splintering or disintegrating altogether.

The movement’s decline comes as states like Arizona passed harsh immigration laws that included provisions allowing local police to question a person’s immigration status while enforcing other laws, Potok said.

Those laws created an impression among some civilian border militia members that state governments were doing more about illegal immigration, and that they no longer had to, he said.

Jennifer Allen, interim director the Arizona chapter of the immigrant advocacy group, the Southern Border Communities Coalition, said that organizations like Ready’s thrive on a charismatic leader, and tend to implode once that leader is gone.

“What brings hate groups together is anger and fear. So it makes sense that they would start to direct that toward one another,’’ she said. “They also attract a lot of people that want to be mega personalities.

“And it ends up being their own worst enemy — fighting over the limelight,’’ she said.

The SPLC also cites the case of Shawna Forde, a former member of the Minuteman Civil Defense Corps. She was convicted in a May 2009 home invasion that left a 9-year-old girl and her father dead.

Prosecutors said the invasion was an attempt to steal drug money to fund her group’s border operations.

Forde was expelled from the Minuteman group in 2007 amid allegations of lying and pretending to be a senior leader. At the time of the killings, she was the head of her own group called the Minutemen American Defense.

The SPLC’s report said the killings cast a pall over the entire civilian border militia movement.