With all the attention to Ohio, Pennsylvania, and West Virginia, it's easy to forget that by February 19, we'd already selected 70% of the pledged delegates heading to Denver, and Barack Obama had already built a nearly unbeatable lead. After yesterday's primary, we've now selected 94% of the delegates, and even though Barack Obama has just endured the toughest stretch of the campaign so far, he's only yielded 6 delegates from his lead.

So as far as delegate math, nothing much changed since February. But what about intangibles, like trends in national support for the Democratic nomination? Here's data from 187 different polls, averaged by month:

You can see the meteoric rise of Barack Obama from November to February, and his steady climb since then. Clinton, on the other hand, has hovered between 42% and 44%.

And most importantly, Barack Obama has led Hillary Clinton since February.

Some additional observations:

• The chart disproves the claim that Barack Obama's support is waning. The regional peculiarities of the nominating calendar may be distorting our perception of "momentum" but there is no indication of any decline in support for Obama on the national level. In fact, his support has actually increased in every month.
• Meanwhile, the chart also debunks the notion that Hillary Clinton has finally hit her stride. Despite her victories and small net delegate gains, her national support now is essentially the same as it was six months ago.
• Although Clinton's base is dedicated and resilient, she has been unable to break the 44% barrier. In all likelihood, that's her peak -- no matter how hard she may climb, she just won't be able to get higher.
  
• The chart suggests that most Barack Obama benefited most from John Edwards' withdrawal -- his support increased 11 points in February, whereas Clinton's only grew by 2 points. (For more on the impact of Edwards withdrawal, you can read Poblano's assessment -- made before Edwards' exit. Poblano concluded Edwards dropping out would help Obama, adding 2-4 points to his national polling totals.)

Ultimately, what this chart tells me is that we learned what we needed to know back in January and February, when it became apparent that Barack Obama was the overwhelming favorite to win the nomination.

Nothing significant has changed since then and there is no indication that anything significant will change in the next few days and weeks as the campaign draws to a close.