Nearly two dozen Democratic presidential candidates paraded through Iowa this weekend, speaking at the state fair, the annual Wing Ding dinner and a forum on gun control. The sheer volume of contenders signals a new phase of the primary campaign, ending the get-to-know-you period and beginning a six-month sprint to the Iowa caucuses. They'll be competing for the support of Democrats who say repeatedly that, despite their differences, their top priority is landing on a nominee who can defeat