David Shribman recently wrote (accurately, as far as I can tell) about “the quiet Republican hope that maverick Sen. Elizabeth Warren will challenge former Secretary of State Hillary Clinton from the left in the Democratic primaries.” The hope, I take it, is that Warren legitimates lines of attack on Clinton, lowers her favorability rating, costs her money, and pulls her further to the left of the median voter. But a Warren primary run would (assuming, as I do, that Clinton would win) also help Clinton in certain ways. It would give her fresh campaign experience and allow her to position herself as a relative moderate who had beaten back a challenger from the left. I suspect that the net effect would be a stronger Clinton.