With polling averages showing that Obama holds a small but meaningful edge in the electoral college in enough states to put him well past 270, Republicans have fallen back on a prediction: A last minute shift in the electorate will put Mitt Romney over the top.

As Mike Allen put it this morning, many Republicans “fear Romney’s momentum has stalled” and are now banking on “some tectonic shift in the country hasn’t been fully detected by pollsters or explained by the press.” This is a variation of the other argument Romney supporters have been making for some time — that a last minute break Romney’s way will ensure another outcome like 1980.

The question, though, is whether the rise in early voting is making this scenario more and more remote.

On a conference call with reporters, David Axelrod derided the “myth of the wave that it’s all going to break in his favor.” He added: “This professed momentum from the Romney campaign is really faux-mentum.”

Obama advisers cited two factors that they say makes the “last minute wave” theory bogus. They argued that Obama’s early voting edge all but ensures that Romney needs to rack up massive margins among the remaining voters. If this is so, it makes the “last minute wave” theory less and less plausible.

Obama campaign manager Jim Messina told reporters that campaign calculations show that Obama’s lead in early voting in North Carolina, Nevada, and Iowa mean that Romney has to win from 54 to 60 percent of the election-day vote in those states to prevail.

The idea that early voting reduces the chances of a last minute tectonic shift is one that hasn’t gotten enough attention, and is worth thinking about.

Axelrod also made a case against the wave I hadn’t heard before: He said undecided voters in the battleground states are tilting towards Obama. “In many of these states, look at structure of undecided vote that remains,” Axelrod said. “They almost uniformly have a more positive view of the President than they do of Governor Romney.”

I’m double checking to see if the data bears that out. For now, keep in mind what Axelrod said the other day: In six days, we’ll know who’s bluffing.