Democrats also faced a political environment that had swung sharply Republican, partly due to a wave of public discontent over passage of Obama's health-care law.
The same Republican surge that helped the party net more than 60 seats in the House — the biggest gains by any party in 62 years — swept in governors and state legislators.
"2010 was a really difficult year for there to be a Republican wave election," said Michael Sargeant, the DLCC's executive director.
The spending and timing paid off for the Republicans, as they won control of 57 legislative chambers, up from 36 before the 2010 elections, and increased their governorships to 29 from 23, according to the National Conference of State Legislatures. In the wake of the 2012 elections, Republicans control 56 state legislative chambers and 30 governorships.
"You can spend hundreds of millions of dollars fighting over a couple dozen congressional districts over 10 years, or you can spend significantly less and impact the shape of those congressional elections over 10 years via state legislative elections," said Chris Jankowski, the president of the Washington-based RSLC, referring to the Republican strategy heading into the 2010 vote. "It was a cost-effective analysis that truly bore out in reality."
Once in office, technology made it easier for line-drawers to consolidate and further their partisan goals.
Map-making software is cheaper, more powerful and widely available, compared to a decade ago. State lawmakers can build databases with detailed voter registration figures, election results and population data to project campaign outcomes and demographic trends.
It may also be easier to predict voter preferences. Party- line voting is increasing: fewer than 30 districts backed the presidential candidate of one party and a House candidate of the opposite party in 2012, the lowest total in at least 90 years, according to data compiled by Bloomberg.
"If you're a map-maker drawing lines, that's just gold for you, because you can very reliably use partisan voting patterns in one election to predict what it might be in another, or much more so than you could before," said Rob Richie, the executive director of FairVote, a Takoma Park, Md.-based nonprofit that wants to change the redistricting process to reduce partisanship in Washington.