Depending on what happens in a smattering of very close races, we’ll probably either be hearing tonight that Republicans made great gains that consummate the decline and fall of the Obama Era, or that these gains were so overwhelming that the proper parallels are the Sack of Rome, the Saint Bartholemew’s Day Massacre, and the New Deal realignment. Yes, interns in the bowels of the MSM may have been assigned an emergency backup memo laying out a substitute “narrative” if it appears Democrats have hung onto Senate control, and/or a famous Republican like Scott Walker is taken off the list of potential future presidents because he’s lost his job. And I don’t know how the wizards will play it if we just don’t know what’s happened by sign-off time tonight thanks to outstanding mail ballots, slow counts and runoff requirements.

In any event, as you prepare for the results and the spin wars, I’d recommend as the best single backgrounder Ron Brownstein’s piece published by The Atlantic yesterday on the “tectonic plates” of this and future elections. Ron very carefully covers such essential topics as the history of second-term midterms (the average loss of Senate seats for parties holding the White House in a second midterm is over seven), the convergence of straight-ticket voting with an unusually pro-Republican Senate “class;” and the “midterm falloff” problem afflicting young and minority voters and hence Democrats. But here’s the data point that’s most important to keep in mind tonight: the demographics of the midterm and presidential electorates are so different that exactly the same performance among different groups that could earn GOPers a “smashing victory” tonight could lead to abject failure in 2016. How do we know this? Because it happened between 2010 and 2012:

[I]f the 2016 Republican nominee wins the same share of whites that polls show the party positioned to capture in the 2014 House races, the Democrat would win the next presidential race—absent meaningful GOP gains with minority voters.

Republicans don’t need to look very far back to grasp that truth. In 2010, the exit polls found that Republican House candidates won 60 percent of white voters (for the first time in the history of polling) and the GOP enjoyed the biggest midterm House gain for either party since 1938. Two years later, Romney virtually matched them by taking 59 percent among white voters and didn’t come close to retaking the White House. Recognizing that reality, two prominent GOP strategists—Neil Newhouse (Romney’s lead pollster) and Glen Bolger—issued a firm warning last week in a Washington Post op-ed: “Winning in a non-presidential-turnout year, when older and white voters make up a larger percentage of the electorate, should convince no one that we’ve fixed our basic shortfalls with key electoral groups, including minorities and younger voters.”

Geography echoes demography, at least when it comes to presidential elections:

Geography sends similar caution signs to the GOP. For all of their likely gains this year, Republicans almost certainly won’t dislodge any Democratic Senate seats from what I’ve termed the Blue Wall: the 18 states Democrats have carried in at least the past six consecutive presidential elections. Even in 2010, when a cresting wave helped Republicans take Blue Wall Senate seats in Illinois, Pennsylvania, and Wisconsin, the party could not follow up by capturing those states in the next presidential race. Although Republicans this year have reaffirmed their ability to compete for states at the edge of the modern Democratic map—Colorado, Iowa, New Hampshire—until they show they can break the Democrats’ hold on some of the core Blue Wall’s 242 Electoral College votes, the GOP will begin the presidential race in a geographic hole. As Newhouse and Bolger wrote, “Republicans were not able to put any Senate races in those Blue Wall states in play. Thus the GOP ‘strategy’ [for 2016] is essentially to be perfect in purple states—not a game plan with a high probability of success.”

Brownstein doesn’t spend his entire column raining on tonight’s planned Republican parade; he clearly thinks Obama’s poor approval ratings and the shakiness of the economy are going to be a problem for Democrats in 2016. But the question remains: can Republicans take advantage of their opportunities then if they delude themselves into believing they’ve won some sort of mandate today?

Look, I understand the temptations of a good election night. Back in 1998 I wound up on MSNBC (not so big a deal then) as a Democratic “analyst” of what was happening in that midterm, and mostly what I did was to grin like an idiot. But then again, that truly was a historic election, insofar as it was the first second-term midterm ever where the president’s party gained congressional seats. I don’t think tonight is going to compare in surprise value, and in may just tell us Republicans are capable of picking up spare change on the ground and Democrats can’t stop dropping it.

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Ed Kilgore is a political columnist for New York and managing editor at the Democratic Strategist website. He was a contributing writer at the Washington Monthly from January 2012 until November 2015, and was the principal contributor to the Political Animal blog.