Time has been cruel to many once-revered political assertions. No, all politics is not local. No, the road to the White House does not lead through New Hampshire. The “solid South” hasn’t been a solid Democratic redoubt since 1944; “rock ribbed Republican” New England has yielded a grand total of four electoral votes for the GOP in the last six Presidential elections.

If you’re looking for a truism that remains true, then reach out and grasp this one: the “six year curse.” With one (highly instructive) exception, the party that holds the White House will lose Congressional seats in the six-year midterms. It happened to Teddy Roosevelt and Franklin Roosevelt; it happened to Ike and LBJ and Reagan. It will almost surely happen to Barack Obama this November.

Why? There is no single reason; there are, rather, different forces, any one of which can afflict the party that’s held the White House for six years. What makes this November so daunting for Democrats is that almost all of them are at work this time. Consider what an honest Obama confidant would tell the President:

If something goes wrong, you own it: Did the economy tank under George W. Bush? Yes. Was his decision to go into Iraq disastrously wrong? Yes. Does it matter this November? No. Iraq and the economy were two huge reasons why Obama won the 2008 nomination and then the general election. But after six years, there’s no strength left to the “it-was-the-last guy’s fault” argument. (The memory of Herbert Hoover helped FDR’s Democrats gain seats in the 1934 mid-terms, but by Roosevelt’s sixth year, the economic contraction cost his party big midterm losses.) If the Taliban’s gaining strength in Afghanistan, and if murderous extremists control large swaths of Iraq, the public knows the buck stops with Obama.

Your strengths matter less: In the fall of 1986, Ronald Reagan was still a popular president, with a Gallup job approval rating of 63 percent, as the arms-for-hostages-Iran-contra story didn’t break until just after the midterms. That’s one reason why Republicans only lost five House seats that fall—a fine showing for a six-year midterm. The Senate was a very different story. Six years earlier (which turned out to be the last time a Presidential candidate had real coattails) Reagan had helped elect 12 new Republican Senators. But with no Gipper on the ballot, seven GOP incumbents lost their seats,(many by very close margins) in states like Alabama, Georgia, Florida, North Carolina, North and South Dakota—all places where Reagan had won huge margins just two years earlier.

By contrast, Obama’s job approval numbers are underwater. But his absence from the ticket will still hurt Democratic Senate candidates in states like Michigan, Colorado, and North Carolina, where aggressive efforts helped turn out large numbers of blacks and Hispanics in his two Presidential runs.

Your party suffers when the public mood is grim: I don’t know how many election cycles have featured reports of an “anti-incumbent” mood that will sweep office-holders of both parties into exile. It may happen someday, just as it’s possible that we will one day see a brokered convention (roughly the same summer I reach the Wimbledon quarterfinals). What’s clear is that, in recent history, it hasn’t happened. When voters think things are going wrong, they figure out—rightly or wrongly—which party to blame. In every midterm with a dyspeptic electorate, their anger has been aimed in one direction. From the post-Watergate November of 1974 to the Republican capture of the Congress in 1994, to the Democrats’ recapture of the Congress in 2006, to the huge GOP gains in 2010, the prevailing party suffered minimal damage at worst. As of now, Mordecai “Three Finger” Brown could count the number of endangered Republican Senate seats on one hand, and have a finger left over.

The “Great Exception” offers you no comfort: So how did the Democrats actually pick up five House seats in 1998, and not lose a single Senate seat, at a time when the incumbent Democratic President had been pummeled all year by accusations of sexual misconduct and possible perjury? On August 17, just a few weeks before the fall campaign iced off, he had to go on national TV to offer a mea kinda sorta culpa.

Yes, part of the explanation was Republican overreach, which, combined with Independent Counsel Ken Starr's imitation of Inspector Javert, brought Clinton’s supporters to the polls. The far more powerful explanation was the now-famous phrase pinned on James Carville’s campaign office wall: it’s the economy, stupid.

Describing the economy in 1998 makes it hard to believe we’re looking at the same country: unemployment at 4.5 percent. Inflation at 1.5 percent. Real GDP growth over 4 percent. The projected budget surplus was so high that a serious economic debate was underway that asked: should we wipe out the national debt, or do we need a bit of debt to keep credit flowing?

As for the national mood? In the fall of 1998, the NBC-Wall Street Journal poll reported that, by a 55-31 margin, the public believed things were pretty much headed in the right direction. All of which meant that while the public may not have trusted Clinton with their young daughters, they did trust him to mind the store.

Today? That same poll reports that, by a 2 1/2-1 spread, the country thinks “things are off on the wrong track.” And the economic numbers show a slow shuffle toward an anemic recovery; certainly not the kind of numbers that would persuade voters to rally behind the President’s party.

It’s not beyond possibility that Republicans could trigger such a rally, say, by seriously pushing impeachment (which may explain why Democrats react to the idea the way Brer Rabbit regarded the briar patch). But if we’re talking about probabilities, that six year curse looks very much like it will live to haunt another second-term President.