Senate Democrats’ and Republicans’ campaign arms would be wise to heed the words of Oscar Wilde, the 19th century Irish dramatist: “To expect the unexpected shows a thoroughly modern intellect.”

With nearly all of the major Senate primaries wrapped up, a series of unexpected events has swung momentum to and fro in the battle for the Senate, with the end result being a landscape offering a path to the majority for both parties.

Earlier this week in Wisconsin, Senate Republicans unquestionably scored a victory when Tommy Thompson won the GOP nomination. Thompson served four terms as governor, so he knows a thing or two about winning statewide races. His moderate political profile makes him more of a threat to win independent voters than any other Republican who ran. And he enjoys virtually universal name recognition in the state.

Thompson managed to win in the same environment that establishmentarians like Sen. Richard Lugar (R-Ind.) and Texas Lt. Gov. David Dewhurst (R) couldn't successfully navigate. A Thompson victory appeared a dubious proposition a few months ago, with conservatives relentlessly slamming him from the right over things like his previous support for an individual health-care mandate.

Equally unforeseen several months ago was Rep. Todd Akin’s (R) nomination in the Missouri Senate race last week, which was a welcome outcome for Senate Democrats. Akin parted ways with his D.C. consultants late in 2011, committed several gaffes and looked like he was destined to watch self-funding businessman John Brunner walk away with the nomination. But with a little help from some unlikely Democratic friends, Akin unexpectedly prevailed in a three-way race. Republicans are still favored to pick up the Missouri seat, but Akin’s unpredictable streak means the party's grasp on it is a bit more tenuous.

So is the Democratic outlook in Nevada, where an ethics investigation surrounding Rep. Shelley Berkley (D) has cast a cloud over a campaign that represents a rare Democratic pickup opportunity this cycle. The House Ethics Committee announced last month it would launch a full investigation into the question of whether Berkley used her position in the House to help benefit the financial interests of her husband. The GOP attack ads on the subject virtually write themselves (and already have).

Finally, virtually no one anticipated Sen. Olympia Snowe’s (R-Maine) sudden retirement announcement in February, a development that threw a seat that was nearly certain to stay in the GOP’s hands into play. Independent former governor Angus King's decision to join the race to replace her was even more good news for Democrats. Party powerbrokers are wagering that King – the overwhelming favorite in the race – would caucus with them if he is elected.

There will likely be a few fall surprises yet to come, which could be equally or even more decisive in the battle for the Senate. The campaigns of Rep. Connie Mack (R-Fla.) and Ohio Republican Treasurer Josh Mandel haven't lit the world on fire, but a flood of outside money hitting their Democratic opponents has kept the two afloat in the polls. If either is able to pull it together for the next 11 weeks, the GOP could compete in swing states not counted among Democrats’ most vulnerable right now.

In Arizona and North Dakota, a pair of strong Democratic recruits, Richard Carmona and Heidi Heitkamp, each have the potential to make their races interesting down the stretch in states that once looked like sure things for the GOP. And in Indiana, Rep. Joe Donnelly (D) is hanging around with Republican state Treasurer Richard Mourdock in recent polling.

All of this is, as they say, why they play the game.

Now, without further ado, to the Line!

(A reminder that the races below are ordered according to likelihood that they will change parties, with No. 1 being the most likely.)

10. New Mexico (Democratic-controlled): This one remains in the 10 spot, but it's at risk of falling off the line. All of the recent polls in the state have shown Rep. Martin Heinrich (D) with a lead on former congresswoman Heather Wilson (R), and this is a Democratic-leaning state. (Caveat: Basically, all the polls have come from Democratic-leaning pollsters.) Meanwhile, the polls in Indiana and Florida show that both of those states are increasingly competitive. We'll keep an eye on it; for now, Wilson's record as a strong campaigner keeps her race on this list. (Previous ranking: 10)

9. Nevada (Republican-controlled): Berkley hasn't led in any poll conducted in the 2012 calendar year, and her ethics issues aren't helping her right now. A race that began as what looked to be a pretty pure toss-up in a pretty pure swing state is now tilting in Heller's favor. But we're still waiting for a good poll to tell us whether Berkley is paying a major price for her problems. For now, it's all in the realm of educated guesses. (Update 12:59 p.m.: The Democratic Senatorial Campaign Committee has now released a poll showing Berkley leading Heller 44 percent to 42 percent.) (Previous ranking: 8)

8. Virginia (D): Virtually every live-caller poll has shown the match-up between former Republican senator George Allen and former Democratic National Committee chairman Tim Kaine to be a tossup. The most recent Quinnipiac University/CBS News/New York Times poll was no exception, showing Kaine with a two-point lead over Allen, an advantage which was inside the margin of error. Both candidates have been pursuing ticket splitters, a rare commodity considering how closely-aligned each is with his party’s presidential nominee. Kaine’s fundraising has been stronger than Allen’s, but that data point is more useful as an enthusiasm gauge, because both sides will have the cash to compete. In a race as close as the polling shows, the “turnout will matter” cliche is especially applicable in the commonwealth. (Previous ranking: 9)

7. Massachusetts (R): Democrat Elizabeth Warren’s most ardent supporters may have been disappointed that she will not be the keynote speaker at the Democratic National Convention. But delivering a speech before Bill Clinton isn’t a bad consolation prize. The convention is also an opportunity for Warren to link herself more closely to Obama. And with polling from the spring showing her winning an unusually small share of the president's supporters, it might be just what she needs. The race remains close, as a late July MassINC poll showed Warren leading Brown by two points, which amounted to a statistical tie. (Previous ranking: 6)

6. Wisconsin (D): While Thompson's win is certainly a win for the GOP, that hardly means this race is over. Wisconsin is still a swing state, Rep. Tammy Baldwin (D) has been raising far more money than Thompson, and the last time Thompson was elected was 1998. The big question now is whether he can rekindle the magic that won him four terms in the 1980s and 1990s and run the kind of campaign one needs to run in 2012. Taking 34 percent in the primary is not a resounding statement from a popular ex-governor; it was good enough, but much remains to be seen. (Previous ranking: 7)

5. Montana (D): Rep. Denny Rehberg (R) has voted against Rep. Paul Ryan’s (R-Wis.) budget twice. But Ryan’s addition to the national ticket has given Democrats a new opportunity to try to tie Rehberg to the House budget chairman in a state with a sizable senior population. At the same time, doing so would highlight where Rehberg has broken with his party, which is an advantage for the GOP here. Both candidates have been underscoring Montana-first themes in TV ads (wolves!) designed as preemptive remedies for membership in an unpopular Congress. But in the fall, outside groups will remind voters about the connections each candidate has to Washington. (Previous ranking: 5)

4. Missouri (D): National Republicans were heartened when Akin's first ad in the general election went negative on Sen. Claire McCaskill (D-Mo.). Akin, in the past, has resisted the urge to run negative ads. But Democrats are giving as good as they get, and they have already launched ads attacking Akin for his past statements in support of Social Security privatization and against federal student loans. This race mirrors the presidential in that, if it's all about McCaskill and Obama, the GOP probably wins; if it's all about Akin, Democrats have a much better shot. (Previous ranking: 4)

3. North Dakota (D): Democrats should be pleased with former attorney general Heidi Heitkamp’s better-than-expected performance so far. But American Crossroads and its allied nonprofit Crossroads GPS continue to hammer her on the air in this Republican state. Romney’s selection of Ryan as his running mate could be an opportunity for Democrats to change the subject from Republican attacks over Heitkamp's support for the federal health-care law to Rep. Rick Berg's (R) votes for Ryan’s budget and its Medicare overhaul. But overall, the fundamentals of this race continue to favor Berg. (Previous ranking: 3)

2. Nebraska (D): Former Democratic senator Bob Kerrey isn’t expected to attend the Democratic National Convention, but that’s not going to be enough to stop GOP attacks tying him to the president. (There is video online of him saying the longer he lives in New York, “the further to the left I get on health care.") Kerrey deserves credit for solid fundraising, but in this red state, money alone won’t be enough to catch Republican nominee Deb Fischer, who has proven to be a steady candidate thus far. (Previous ranking: 2)

1. Maine (R): A new Republican-leaning poll here shows King's lead isn't as big as earlier polls had it. The Moore Consulting poll has King leading Secretary of State Charlie Summers 46 percent to 28 percent. But that's still a sizeable lead, and more importantly: Democratic nominee Cynthia Dill remains mired in the single digits (8 percent). Republicans need her to rise in the polls and cut into King's numbers, but so far, there is little indication that she's doing that. She did recently get the backing of former governor John Baldacci (D), but Baldacci left office with very poor approval numbers, so we're not sure how much that helps. (Previous ranking: 1)