To be fair, a lot of the disagreement stems from semantics—the definition of the word “wave.” Cohn argues that if Republicans merely sweep red-state Democratic seats and perhaps pick off a stray swing seat, it’s not a wave election—even if Republicans net seven seats on their way to the majority. To accomplish that feat, Republicans would need to oust four sitting Democratic senators. Over the last decade, Republicans have defeated only three sitting senators (Tom Daschle in South Dakota, Russ Feingold in Wisconsin, and Blanche Lincoln in Arkansas). Surely, a red-state sweep would signify the conclusion of a political shake-up in the South, where voters are so disgusted with the national Democratic Party that they’re willing to throw out senators who had previously relied on split-ticket voters to win. If a Republican takeover by picking up seven Senate seats isn’t a wave, it’s awfully close.

There’s also a methodological conflict at hand. Most political scientists define a wave in terms of House seats gained, because Senate contests only take place in one-third of the country. But in the House, gerrymandering and voter self-sorting have limited the universe of competitive seats. With a 234-seat majority, Republicans have already come close to hitting the upper limit of their representation. Emory University political scientist Alan Abramowitz found that even a sizable 5-point generic-ballot advantage for Republicans would net them only 15 House seats. The Cook Political Report, assessing a “2010-lite” environment for Republicans earlier this year, expects GOP gains of just two to 12 House seats. It’s very possible Republicans could exceed expectations in the Senate while adding only marginally to their House majority.

Still, there’s plenty of race-by-race evidence to suggest that most contests are trending in a Republican direction. Over the past several months, the Iowa and Colorado Senate races have turned from long shots to promising Republican pickup opportunities. In Iowa, Republican nominee Joni Ernst is running evenly with Democratic Rep. Bruce Braley in the Real Clear Politics polling average, a marked shift over the last two months. And in Colorado, Democratic Sen. Mark Udall only holds a 1-point average lead over GOP Rep. Cory Gardner, according to RCP, in a race that’s shaping up to be a barn burner.