A new national Democratic primary poll from Diageo/Hotline (.pdf) (March 28-31, 342 Dem RV, MoE +/- 5.3%) shows Obama leading Clinton by 12 points, after the two had remained close in similar polls in previous months. On negative campaigning, 42% felt Clinton had unfairly attacked Obama, while 22% felt Obama had atttacked Clinton unfairly.

Obama 50
Clinton 38

Obama leads by 5.2-points in the RCP Nat'l Average

The poll also matched up the two Dems against John McCain (799 RV, +/- 3.5%).

McCain 46 - Obama 44
McCain 50 - Clinton 41

In the RCP Nat'l Avgs., Obama leads McCain by 0.2 points, and McCain leads Clinton by 2.4 points