First, today's National Trackers:
Rasmussen
Obama 51 Clinton 40
Gallup
Obama 51 Clinton 43
And the graph of the combined national trackers over the past 3 weeks:
Yesterday, Obama hit upon a number of records in the national tracking polls. It was the first day that he was 50% or more in BOTH polls. Furthermore, it was also the largest combined lead he has had in the history of the race.
Today, Obama continues to hold over 50% in both polls and his lead over Clinton is identical to yesterday.
Poblano, over at 538.com (which I highly recommend reading every day), had an excellent post this Sunday titled "The Momentumless Primary." In the post, he wrote:
A week ago, Barack Obama led Hillary Clinton by 10 points in the Gallup Daily Tracking Poll. I asked the readers whether they expected today's poll -- it's April 6th -- to show a lead of greater than 10 points for Obama, or fewer.
...
But most people did not take the bait, and said they expected Obama to be fewer than 10 points ahead. Which, as it turns out, was the right answer. In today's Gallup Tracker, Obama is 3 points ahead of Hillary Clinton.
Most people who took the under cited the principle of "regression to the mean". And this is an underrated dynamic in analyzing polls. Ninety-five percent of polls, theoretically, fall within the margin of error established by the pollster. The flip side to that is that 5 percent don't.
If only he had waited one more day the pose the question about the Gallup Poll. In any case, Obama has had a large and sustained national lead in the trackers for the last 2 weeks, so even on Sunday when Obama was at the lowest polling point in a week, Clinton was still trailing by 7.5% in the combination of the two trackers. Clearly regression to the mean is not being observed when we look at the aggregate of both trackers.