It may be some time before we understand the motives of the brothers allegedly responsible for last Monday’s bombings at the Boston Marathon, if we ever do.

All week, even as some media outlets reported descriptions and arrests of supposed suspects, only to retract those reports later as inaccurate, cooler heads cautioned against speculating about the perpetrators of the bombings and their motives.

Unfortunately, as we’ve learned over the past four years, “cooler heads” does not describe people bent on depicting tea partyers as violent enemies of the state.

From MSNBC, (taxpayer-funded) NPR and other precincts, we heard chin-stroking “analysis” of the fact the attack took place on Tax Day … and around the anniversary of the FBI’s raid on the compound in Waco, Texas, and the Oklahoma City bombing … and near the date of Hitler’s death …

In short, they seized on anything that lent an iota of credibility to a premise they can’t seem to drop: “Extremists” on the right, in which group they include the tea party, are liable to inflict mass violence on America at any time.

Typical was this tweet by left-wing filmmaker Michael Moore, who never met a narrative-building falsehood he could resist: “Tax Day. Patriots Day.”

He didn’t have to spell out T(axed) E(nough) A(lready) Party Patriots. Everyone knew what he meant.

The Boston Marathon was an odd target for supposed anti-government anarchists, as opposed to a federal building like the one actual anti-government anarchists Timothy McVeigh and Terry Nichols blew up in Oklahoma City. Still, speculation about the significance of April 15 would have been almost understandable — almost — had this been the first time liberal commentators conflated killers and tea partyers:

  • Multiple national news outlets included tea-party references in early stories about Joe Stack, who in February 2010 flew a small plane into an IRS office in Austin, Texas. His suicide note, however, included rambling accusations against large companies, the Catholic Church and George W. Bush, as well as approval for what he called "the communist creed."
  • When Jared Lee Loughner went on a January 2011 shooting spree in Tucson, Ariz., killing six people and injuring more than a dozen, including U.S. Rep. Gabrielle Giffords, liberal commentators not only assumed Loughner was a right-winger but accused tea-party favorite Sarah Palin of provoking the attack by placing a bulls-eye on Giffords' district on a map of election "targets" in 2010. Further examination revealed that — like that of most mass killers — Loughner's politics was an incoherent muddle of radical, conspiratorial beliefs.
  • After the movie-theater shooting in Aurora, Colo., last summer, Brian Ross of ABC News reported a man with the same name as the shooter had registered with a local tea party. Of course, "James Holmes" — the alleged shooter's name — is a rather common name in America. The link was false.

There are more such examples of false tea-party links to violence in just four years. One is left to conclude either the people making these links are incapable of objectivity or understanding when it comes to the group, or they don’t mind smearing the group’s reputation while the facts are found.