Opinion: Have Democrats already lost the Senate? Nope.

In my column on Wednesday, I wrote about the Democrats’ chronic difficulty in getting “unreliable voters” to turn out for midterm elections – like the one next month that will determine who controls the U.S. Senate and the agenda for President Obama’s last two years in office.

I noted one oft-cited measurement of which voters are likely to turn out: the “enthusiasm gap,” which this year shows Democrats less fired up than Republicans. They’re significantly less fired up in some polls, marginally so in others, but it’s a consistent finding in general.

Still, that doesn’t mean Sen. Mitch McConnell (R-Ky.) should begin measuring the drapes in the Senate majority leader’s office yet.

Here are three reasons the Senate election is far from over:

[1] National polls don’t matter, and state-by-state polls aren’t as reliable.

Those national numbers about enthusiasm are interesting, but they don’t matter if Democrats in states with close Senate elections are more engaged than their inattentive colleagues elsewhere. There’s not much public polling on enthusiasm levels in individual states -- and the horse race polling is sparser (and sometimes less reliable) than in a presidential election.

[2] There are plenty of wild cards on the landcape.

In Kansas, a state Republicans expected to keep, independent challenger Greg Orman appears ahead of incumbent Sen. Pat Roberts (R-Kan.). In South Dakota, independent candidate Larry Pressler has turned another expected GOP victory into a three-way muddle. In Georgia, Democrat Michelle Nunn appears to be gaining ground on Republican David Perdue. In Iowa and North Carolina, public polls show virtual ties, with results within the margin of error. Those are enough unknowns to make the Senate outcome unpredictable.

[3] Enthusiasm isn’t everything; votes are all that count.

Polls on enthusiasm tell you about the mood of the electorate, but they can’t tell you which voters will actually show up. On election day, the grudging vote of an unenthusastic mope counts just as much as the most zealous volunteer’s.

That’s why one of the most important (but least visible) parts of this campaign is each party’s effort to turn their voters out, no matter how unenthusiastic they are. The Democrats, in particular, have launched an ambitious $60-million project to expand the midterm electorate – which is a high-minded way of saying: “prod more Democrats to the polls than usual.”

A half dozen states with relatively small populations could decide the outcome in the Senate. Alaska and South Dakota have fewer than half a million registered voters each; New Hampshire, Kansas, Arkansas and Iowa have fewer than 2 million. (All six combined have fewer than half as many voters as California.) So a relatively small organizational effort in any of those states could have an outsize impact

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