While there is no evidence that a national partisan wave will develop between now and Nov. 6, there is every reason to expect a number of "state waves" that will prove to be challenging for some candidates - and for political handicappers.
In fact, candidates' abilities to fight through the waves in a handful of states could well determine which party controls the Senate.
In a number of Senate contests, a strong candidate faces the daunting task of running 10 or 15 points ahead of his or her party's presidential nominee. That isn't impossible, but it certainly is challenging.
For Sen. Scott Brown in Massachusetts, Heidi Heitkamp in North Dakota, Sen. Jon Tester in Montana, Rep. Joe Donnelly in Indiana, Linda Lingle in Hawaii and Linda McMahon in Connecticut, the fundamental political landscape in their states is not flat. Instead, it's strongly tilted against them.
Then-Sen. Barack Obama won Massachusetts by more than 25 points and Connecticut by more than 22 points in 2008, and while his victory margins are likely to be smaller this time, he will still carry both states comfortably. The same goes for the state where he was born, Hawaii, which he carried by more than 45 points four years ago.
Obama lost North Dakota four years ago by almost 9 points while he was winning nationally by more than 7 points, and this time the president is likely to lose the state far more resoundingly. In 2000, in a very close contest nationally, George W. Bush defeated Al Gore by more than 27 points in the Peace Garden State.
Two states that saw close races in 2008 appear likely to blow open this time. Obama lost Montana by just over 2 points four years ago, but a double-digit win in the state by Mitt Romney seems in the cards this year. Neither Gore in 2000 nor John Kerry in 2004 drew even 40 percent of the vote in Montana.
And while Obama won Indiana narrowly in 2008 (by a single point), nobody on either side of the aisle expects a tight presidential contest this time. Another double-digit GOP win, much like 1988, 2000 and 2004, seems likely.
Brown, Heitkamp, Lingle, Tester, Donnelly and McMahon all know that to win election to the Senate they will have to win despite their presidential nominee's showing, not because of it.
Interestingly, in at least four of these contests - and maybe even in all six of them - the candidate who must overcome a partisan disadvantage this year is the better candidate and is running the better campaign.
Republicans and Democrats alike are nearly unanimous in praising Heitkamp's campaign and messaging. She is better liked than Republican Rep. Rick Berg, and she has so far been able to run about even with the Congressman even as GOP strategists try to tie her to the president. One Republican consultant claims that Heitkamp "is running the best campaign in America."
In the Bay State, Brown is a more personally appealing candidate than challenger Elizabeth Warren, and observers continue to give the Republican's campaign higher marks than the Democrat's. Warren clearly mishandled the issue of her ancestry.
In Indiana, early favorite Richard Mourdock, who clobbered veteran Sen. Dick Lugar for the GOP nomination, is widely seen as being far less agile and appealing as a candidate than Rep. Joe Donnelly (D). The Democrat won re-election to his House seat in 2010 by distancing himself early and repeatedly from his own party leaders in Washington, D.C., and Mourdock can be sour and off-key in his comments.
In Connecticut, businesswoman Linda McMahon, who lost the 2010 Senate race by a dozen points in a great Republican year (nationally, but not in the Nutmeg State), has remade herself and is running about even against Rep. Christopher Murphy (D). Unlike 2010 Democratic Senate nominee Richard Blumenthal, Murphy isn't known nearly as well statewide as McMahon, and the Congressman's prospects weren't helped by unflattering stories in state newspapers last week about financial missteps.
In the Treasure State, incumbent Sen. Jon Tester (D) is widely believed to be running a better campaign than Rep. Denny Rehberg (R). Tester continues to run strong TV spots that add to his image as a "Montana Democrat," not a national Democrat, while Rehberg's ads either rebut Tester's charges or link the Senator's voting record to Obama.
Of course, none of this answers the question of whether these strong candidates will, at the end of the day, win in difficult partisan territory and in a polarized presidential environment.
All six of the candidates will have to overcome a drag at the top of the ticket in their states, but ticket-splitting isn't unusual in this country.
In 2000, for example, Bush carried North Dakota by more than 27 points (61 percent to 33 percent) over Gore at the same time that Democratic Sen. Kent Conrad was winning re-election by more than 22 points (61 percent to 39 percent) over a weak Republican challenger.
Four years later, the state's other Democratic Senator, Byron Dorgan, was re-elected by more than 36 points (68 percent to 32 percent) in a noncompetitive race at the same time that Bush was being re-elected by 27 points (63 percent to 36 percent).
In the Hoosier State, in 2004, then-Sen. Evan Bayh won by 24 points (593,000 votes) at the same time that Bush was carrying the state by more than 20 points (510,000 votes).
Still, the country is more polarized than it was even just eight years ago, and Republicans didn't have formidable nominees in the 2000 North Dakota race or the 2004 North Dakota and Indiana races. This time, Brown, Heitkamp, Lingle, Tester, Donnelly and McMahon all face credible opponents with enough resources to win. And that makes the job of defeating them more difficult.
This year's battle, pitting quality candidates and campaigns against a state's partisan fundamentals and presidential preference, will go a long way to determining control of the Senate for the next two years.
Stuart Rothenberg is editor of the Rothenberg Political Report.