As teachers inch closer to a walkout on April 2, it's worth looking back at the state question that ultimately made it very difficult, if not impossible, for Oklahoma legislators to pass legislation that would raise revenue. It was State Question 640, which was approved by Oklahomans in 1992 and severely limits the Legislature's ability to raise taxes. "Any tax increase that passed the House and Senate with less than a 3/4 majority would have to go to a vote of the people durin...