intro: It's trite to say a major crisis or tragedy changed everything. But the Boston Marathon bombing occurred smack in the middle of an extraordinarily active political season. Some big initiatives suffered setbacks in its wake, and a few new ones -- welcome back, national-security politics, and we can't wait to learn how Chechnya matters to us now -- are suddenly urgent. Here's some of what the ABC News political unit will be tracking this week.
title: Immigration Nation