One of the core group of supporters for President Obama is 2008 was the “Youth Vote”.

New polling data suggests that far fewer young people are planning to vote at all in 2012, and those that do are not planning to pull the lever for the President in quite the same numbers.

In 2008 young voters chose Obama over McCain by 66% to 32%. Today he leads Romney by 49% to 41%.

Thursday night at the Democratic convention, President Barack Obama could continue relentlessly assaulting Gov. Mitt Romney, put the best face on his own record, or offer a substantive vision for the future. But no matter what themes he emphasizes, we know his acceptance speech will target groups that propelled him to victory in 2008 and remain critical to his re-election, especially Hispanics, women and young people.

An article by Karl Rove in the Wall Street Journal provides additional details:

Then there are voters ages 18 to 29, among Mr. Obama’s most important supporters in 2008. The roughly 23.7 million “millennials” who voted in 2008 were 18% of the electorate, up 2.9 million voters over the previous presidential race. They gave Mr. Obama 66% to Sen. John McCain’s 32%, according to exit polls. This margin of roughly eight million votes was a major chunk of Mr. Obama’s overall edge of 9.6 million.

But youthful enthusiasm for Mr. Obama has waned. In October 2008, 78% of voters 18-29 told Gallup they would definitely vote that year. Now it’s 58%.

There’s also evidence that fewer younger people are registered. A November 2011 study from Tufts University found that 43% of the decline in Nevada’s voter rolls since 2008 came from voters ages 18-24. Similarly, while North Carolina’s rolls rose by 93,709 over that period, more than 48,000 younger voters were dropped from the rolls, 80% of them Democrats.

Mr. Obama’s lead over Mr. Romney in the latest JZ Analytics poll among voters ages 18-29 is 49% to 41%. If young voters turn out this fall in the same numbers as in 2008 and give Mr. Obama this eight-point margin, it will take 2.8 million votes from Mr. Obama’s total and add more than 3.3 million to Mr. Romney’s tally.

Why does Mr. Obama dramatically trail his 2008 performance among younger voters? …Mr. Obama’s biggest problem with millennials is almost certainly his failure to reignite the economy. Robust growth is needed to create the new jobs they need