It’s very clear that the 2010 midterm elections will revolve around turnout patterns, not some big change of public opinion since 2008. Intensifying an already strong tendency in midterm elections, Republicans and Republican-leaning independents at present are looking marginally more likely to vote than Democrats and Democratic-leaning independents. Here’s how Tom Jensen of Public Policy Polling expresses it:

There continues to be no doubt this fall’s election will have more to do with whether Democrats can turn out Obama voters than keep them in the fold. Very few voters are shifting their allegiance from the 2008 election- 8% of Obama voters say they’ll vote Republican this time but an almost equal 6% of McCain voters say they’ll vote Democratic this time. When it comes to voters switching sides it’s basically a wash, but Republicans are doing well across the country due to Democratic disengagement.

So voter enthusiasm matters, particularly when it happens to coincide with the longstanding pattern in midterm elections of older, white voters turning out at significantly higher levels than young and minority voters, who were a big part of the Democratic base in 2008. But how’s about all the talk about “excitement,” and the exceptional energy the Tea Party movement is said to have brought to the Republican Party? Here’s Jensen again:

Among voters who are ‘very excited’ about voting this fall Republicans hold a 52-40 advantage. How much that matters is up for debate though. Scott Brown led the Massachusetts Senate race 59-40 with ‘very excited’ voters but won by only 5. Chris Christie led the New Jersey Governor’s race 60-34 with ‘very excited’ voters but his final margin of victory was only 4 points. As I’ve said before unexcited voters count the same as excited ones and our polling so far this cycle has suggested the Democrats who answer our surveys vote, whether they’re excited about it or not. So I’m not sure how much the wide GOP advantage with ‘very excited’ voters really matters.

So to sum it up, enthusiasm matters up to the point that it motivates someone to vote. Beyond that, a vote’s a vote, and you only get to vote once. It’s a simple point, but one often lost on people in both parties who value “energy” and “excitement” a bit too much. Unless their mood is communicable, or translates into campaign activity of some sort, super-psyched voters who snake-dance to the polls as part of some “movement” have no more weight that those who hold their noses and vote unhappily. That’s worth remembering next time you see one of those measurements of voter “excitement.”