The Split

As you've probably heard, Al and Tipper Gore, after 40 years of marriage, are divorcing. Whenever I hear of a long-time couple separating, I wonder what caused it. You'd think they'd know each other well enough by now. Was it something in particular that caused it, or has there been a problem for years that finally made them say "we've gone this far, but no further"? You'd figure after this long, they could just tough it out.