After days in which some Democrats and their supporters in the press assigned blame for the violence in Tucson on Sarah Palin, the Tea Party, Rush Limbaugh, and Republicans in general, President Obama says “none of us can know exactly” why accused killer Jared Loughner attacked Rep. Gabrielle Giffords and 19 others last Saturday.

“None of us can know exactly what triggered this vicious attack,” Obama said.  “None of us can know with any certainty what might have stopped those shots from being fired, or what thoughts lurked in the inner recesses of a violent man’s mind.”