Larry J. Sabato is university professor of politics and director of the University of Virginia Center for Politics, which publishes the online, free Crystal Ball politics newsletter every Thursday, and a contributing editor at Politico Magazine. His most recent book is The Kennedy Half-Century: The Presidency, Assassination, and Lasting Legacy of John F. Kennedy.

Last week, Republican primary voters passed their first Senate test, producing a North Carolina nominee, Thom Tillis, who is merely imperfect, not catastrophic. After the disasters of recent years, national Republicans will happily take it.

The North Carolina result did nothing to change the expectation among most observers that the Republicans have a 50-50 or better shot at taking the Senate majority. It might even have enhanced those odds. The conventional wisdom is reasonable: We know that the president is unpopular, the president’s party typically performs poorly in midterms and the Democrats are overextended on this year’s Senate map. One of the ways the Republicans could hurt their chances is by running bad candidates in some of these races. Tillis might turn out to be that kind of candidate, but he was clearly the most credible nominee in the primary field.


So where is the Senate right now? Hypothetically, there’s still a wide range of potential outcomes – and all the likeliest ones involve at least some kind of Republican wave, perhaps delivering the magic six-seat gain that would dethrone Democratic Senate Majority Leader Harry Reid.

Let’s adopt a mariner’s, or a meteorologist’s, terminology to make sense of the situation. Democrats hope for no wave at all: Something akin to “beach week,” the post-finals getaway that some of my University of Virginia students are celebrating this very instant on the Atlantic seaboard. Beach week for the Democrats, though, is about as likely as the undergrads’ dream of putting off adulthood. More realistically, Democrats can hope for fearsome-sounding waves that crash loudly but do little structural damage. Republicans, on the other hand, are rooting for an impressive tidal wave, if not a full-fledged historic tsunami.

The following table offers a wide range of Senate outcomes, along with their likelihoods.

*Two independents who caucus with the Democrats, Sens. Angus King (I-ME) and Bernie Sanders (I-VT), are included in the Democratic total.

Some of these scenarios have virtually no chance of happening, particularly the ones where Democrats play even in the Senate or even gain a seat. The Democrats have only a couple real chances to play offense, and their odds in either case are not great.

The two Republican primary candidates the establishment fears most in the open GOP seat in Georgia – Reps. Phil Gingrey and Paul Broun, who have inspired headlines with the words “Todd Akin 2.0” – are lagging behind other, more electable candidates in polling ahead of the May 20 primary and a likely runoff. A solid GOP candidate there should be able to beat Democrat Michelle Nunn in a Republican state in a Republican year. The same goes for Senate Minority Leader Mitch McConnell in Kentucky: Polls there are close, but this is a Republican running on very Republican turf. These races are competitive, but they are not tossups, either.

Meanwhile, there are 14 Democratic seats that are at least marginally practical targets for Republicans. The bigger the wave, the greater the number that could sink come Election Day.

The table above suggests a best guess as to how these seats would fall to the GOP. But let’s be a bit more explicit about it. The next table ranks the 14 Democratic seats in order of their likelihood of flipping parties:

*Walsh was appointed to the seat, which was formerly held by Sen. Max Baucus.

Generally speaking, two factors explain these rankings: President Obama’s average performance in these states in 2008 and 2012, and whether an incumbent is running. But that doesn’t explain all of it: There’s more than a little judgment involved, too.

Two open seats, South Dakota and West Virginia, are at the top of the list. The Mount Rushmore State is ahead of the Mountain State because while Republicans have good likely nominees in both places, ex-Gov. Mike Rounds has run statewide before, and Rep. Shelley Moore Capito has not. National Democrats also have shown little interest in backing likely nominee Rick Weiland in South Dakota, while they are more bullish on Secretary of State Natalie Tennant in West Virginia, which also has a long history of electing Democrats to the Senate. (South Dakota’s record is more mixed.) In any event, these two seats are probably gone for the Democrats even if President Obama and his party bounce back in a big way over the next several months. A “ripple” is enough to wash them away.

Then comes Montana: Sen. John Walsh is an incumbent, but an appointed one. Appointees have a mixed track record of success in winning a full term. Freshman Rep. Steve Daines, Walsh’s likely Republican opponent, won statewide in 2012 (Montana has only one House seat) and is arguably better known. That’s why Walsh is more endangered than senators in redder states like Alaska, Arkansas and Louisiana, and the limited polling we have backs that up. If the Democrats stop the wave here, they will have had about as good an election night as one could reasonably expect.

As the wave builds, next comes Arkansas and Louisiana.

Sen. Mark Pryor of Arkansas sits in very unfavorable terrain: Obama did the worst here of any of the competitive Senate states: The president’s 2008-2012 average was 37.9 percent, worse than even West Virginia’s two-election average. Our Crystal Ball ratings had recently leaned this race to Rep. Tom Cotton, Pryor’s Republican opponent, but we now look at it as a tossup, the same rating we have in Alaska, Louisiana and North Carolina. Pryor has led several recent polls—though it’s hard to believe he’s up by 11 points, as an NBC/Marist survey reported on Monday—and the senator appears to be in an improved position from several months ago. But the state is also just very tough for a Democrat these days.

The same can be said for Louisiana and Sen. Mary Landrieu, although she’s helped by Louisiana’s slightly bluer shade of red (2.4 points better on average than Arkansas over the last two elections, and Obama actually did slightly better in the Pelican State in 2012 than 2008) and by a general election that functions as an all-party primary. Louisiana Republicans say they have never been more unified behind a Landrieu challenger – Rep. Bill Cassidy – but don’t tell that to Sarah Palin, who just endorsed one of the other Republicans, retired Air Force Col. Rob Maness. The likeliest outcome appears to be a December runoff, as Cassidy is likely to lose some GOP votes to other Republicans in the November all-party primary and Landrieu is polling under 50 percent.

Assuming Republicans win every one of these races—a big assumption—we’re now up to five new seats. So the deciding state in the Senate could be Alaska. It’s a Republican but quirky state—just look at its three-way 2010 Senate contest. Sen. Mark Begich could be helped by some ballot initiatives now on the November ballot, which might be a factor in a state where the winner might only need 125,000 or so votes to win.

That’s about a tenth of the votes required to win North Carolina, which presents tremendous turnout problems for Democrats but is also much more politically competitive at the national level than any of the aforementioned states, all of which except Georgia were won by Mitt Romney by 13 points or more. With just a two-point Romney margin, North Carolina was effectively a Republican-tilting tie the last general election. Although a midterm environment is different from a presidential one, simple partisan fundamentals tell us Sen. Kay Hagan has a better (though still middling) chance to survive than her fellow red-state Democrats.

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Democrats, or at least the more optimistic ones, might argue that I’m overstating the GOP’s chances. After all, Republicans were widely expected to gain several Senate seats in 2012 and ultimately lost two. But Democrats had the ocean winds at their backs in 2012. Not only did President Obama end up winning a decent-sized re-election, but many Republican Senate candidacies fell flat.

The late February 2012 retirement of Sen. Olympia Snowe, the Maine Republican, also changed the calculus, transforming a safe Republican seat into what amounted to a Democratic pickup due to the election of independent Sen. Angus King. This year’s late developments, however—like the entrance of Rep. Cory Gardner and former Massachusetts Sen. Scott Brown into, respectively, the Colorado and New Hampshire Senate races—ought to benefit Republicans. Neither may win, but the late entries have improved GOP chances and give them a couple of different potential pathways to a six-seat gain in case some of the aforementioned red-state Democrats prove immune to the nationalization of their races.

Of course, Republicans hope for more than a narrow majority, partly because they might need a cushion of seats to prepare for possible Senate losses in 2016, when the map favors Democrats. Much of the GOP base seems convinced that gale-force winds will enable them to take at least two additional seats, such as Iowa and Colorado. This is conceivable in Iowa’s open-seat contest, if the GOP picks an electable candidate from its field of five. Should no one win 35 percent in the party primary, however, an activist-dominated convention will decide the Republican nomination.

In Colorado, Sen. Mark Udall is the most vulnerable Obama-state Democratic incumbent. He faces a major challenge from Gardner, and polling suggests it will be a hard slog. Iowa seems a likelier possibility to fall than Colorado primarily because it’s an open seat; Democrats might also benefit from the Centennial State’s new election system, which automatically sends a mail ballot to every voter and should increase Colorado’s turnout.

Should a tidal wave develop, the next two Democratic seats in its path are Michigan and New Hampshire. But Michigan, despite being an open seat, is not as good a target as Colorado for Republicans because the Wolverine State is simply more Democratic: Obama’s 2008-12 average is three points better there than in Colorado. That said, Gov. Rick Snyder, the Michigan Republican, could create some coattails for Terri Lynn Land, his Senate ticket-mate, in a state that has only elected one GOP senator since the late 1970s (in 1994). As for New Hampshire, Democratic Sen. Jeanne Shaheen remains a slight favorite. Not only does she have a built-in incumbent advantage, she has a mostly successful electoral history and might be able to cast Scott Brown, the former Massachusetts senator who moved up north to challenge her, as a carpetbagger. Brown also is well known in the Granite State, but he puts off some New Hampshirites who resent ex-Bay Staters’ increasing influence in their state. Still, New Hampshire has been downright schizophrenic politically in recent years, flipping the party identification of its entire House delegation in 2006, 2010 and 2012. So who knows?

The most bullish Republicans foresee a tsunami that even drowns Democratic Sens. Al Franken of Minnesota, Mark Warner of Virginia and Jeff Merkley of Oregon. Plenty of polling has indicated that these three seats could prove competitive. But it would be a shock if Republicans picked up any of them. In Minnesota, Democrats managed to win the state’s governorship even in the midst of 2010, which suggests the Land of 10,000 Lakes has become pretty solidly blue, and despite Franken’s razor-thin election in 2008 the state’s top Republicans passed on challenging him. In Virginia, Warner remains relatively popular, and he might have the most financial resources of any Democrat running this cycle. Oregon is even less likely to flip. From 2008 to 2012, Obama did better in here than in any of the other competitive Senate states. Should she win the Oregon Republican nomination, Monica Wehby might pose a challenge to Sen. Jeff Merkley. But basic partisan realities tell us she will have to be a perfect candidate to win, and there are some early indications that she’s not. Oregon also has all-mail voting, which is helpful to Democratic turnout.

The calculated takeaway is this: As of now, Democrats are clear underdogs in the two states where they want to play offense. They also are probably no better than 50-50 in any of the seven red states where they are defending seats, and drowning in a couple. A big enough wave could cut into the blue states, too, although probably not as deeply as Republicans fantasize. Put it all together, and the current forecast calls for a wave that’s more than a ripple but less than a tsunami – a four to eight-seat addition for the Republicans, with the higher end of the range being a shade likelier than the lower. For Harry Reid, that would be a big-enough splash.