By ALEX ISENSTADT | 6/19/13 5:05 AM EDT

Democrats fell far short of winning the House in 2012, an otherwise banner year for the party, and many are privately glum about taking back the chamber in 2014.

But that grim immediate outlook raises a far more troubling longer-term prospect for Democrats: that the newly drawn congressional lines have tilted the electoral playing field so decisively in the GOP’s favor that the party could control the House through 2020.

That this, in other words, could be the Democrats’ Lost Decade.

Three of the past four elections have produced partisan upheaval, so political forecasting must be approached with caution. Democrats say projecting beyond next year, let alone next month, is a fool’s errand.

But strategists in both parties say they are still reckoning with the long-term implications of Democrats’ disastrous performance in 2010. Not only did they lose the House that year, but setbacks in state capitals meant that Republicans controlled the once-a-decade process of line drawing in 213 districts — nearly five times the number of districts Democrats had oversight over. And Republicans used that power with a vengeance.

The GOP effectiveness in erecting a gerrymandered fortress has created a paradox: Even in a fast-changing electorate, with many demographic trends favoring Democrats, the part of the national government that the Founders imagined would be most responsive to shifts in public opinion and voter behavior may actually be the least responsive.

The possibility of a decade or more of GOP House dominance is something Democrats – and even some Republicans, who still need to hit up donors – are loathe to talk about publicly. But make no mistake: Even as they struggle in presidential and Senate races, Republicans have a structural advantage in the House that could last through the next four elections.

Karl Rove, George W. Bush’s political architect, stopped short of predicting that the speaker’s gavel will remain in GOP hands through 2020. But he said the dual factors of sharp Republican line drawing and population shifts provided a solid foundation for the party.

“The impact,” he said, “is certainly favorable to Republicans at the congressional level.”

Of the 435 districts that constitute the chamber, 242 tilt toward Republicans while 185 favor Democrats (another eight are evenly divided). In November, Mitt Romney – despite getting shellacked nationally – won 21 more congressional districts than President Barack Obama.

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