Politico warns that Barack Obama has a problem he never saw in 2008 — and it’s getting worse.  Mitt Romney’s likely voters are much more enthusiastic than his, and these numbers mainly came from polling data collected before Obama laid a debate egg in Denver:

A new POLITICO/George Washington University Battleground Tracking Poll of likely voters shows ahead of Mitt Romney 49 percent to 48 percent nationally, a statistical tie and a percentage point closer than a week ago.

The head-to-head numbers have held remarkably steady through the past three weeks, but there’s been a notable shift of intensity from the Democrats to the Republicans since the party conventions over a month ago. Most of the poll’s calls were made before Romney’s strong performance at the first presidential debate in Denver.

Only 73 percent who support Obama say they are “extremely likely” to vote, compared to 86 percent who back Romney. Likewise, 84 percent of Republicans say they are extremely likely to vote, compared to 76 percent of Democrats.

Among those extremely likely to vote, Romney actually leads Obama 52 percent to 46 percent. That’s up from a 2-point lead last week. Obama led 50 percent to 47 percent among this group three weeks ago.

Intensity seems to be falling across the board among Democratic constituencies.  Only 71% of African-Americans and 70% of Latinos consider themselves “extremely likely” to vote, well below the topline of 79%, and only 68% of Obama’s key 2008 demo of young voters feel the same way.  By contrast, 82% of white voters consider themselves “extremely likely” to vote, and 77% among seniors.  As James Hohmann notes, this means that Romney can do more outreach to the middle, while Obama now has to try to rally his coalition to turn out — and could turn off independents with that effort.

Other internals look bad in the poll.  Obama’s firm re-elect number on Q6 is only 46% with just four weeks to go before the election — and again, mostly from before the debate.  That’s a low number for an incumbent at this stage of the race, as undecideds usually break hard for the challenger.

That’s even more true when one takes into consideration the sample breakdown in this poll.  It has a D/R/I of 38/30/32, for a D+8.  That’s more Democratic than 2008’s D+7, which took place in a cycle with much more Democratic enthusiasm than this poll demonstrates.  If Obama trails in a D+8 poll by 6 among the extremely likely voters with four weeks to go, he’s in deep trouble — and his debate performance certainly won’t boost him.