Republicans won big on Tuesday night – as much as by who actually voted as who didn't. Here are the takeaways from the exit poll data. (Pamela Kirkland/The Washington Post)

Republicans said Thursday that their midterm triumph shows they have caught up with Democrats in mobilizing voters on the ground, a top priority for the party after it failed to win the White House in 2012.

GOP strategists said they spent two years quietly assembling a permanent field operation that expanded their electorate and targeted voters with more precision. Democrats had touted their multimillion-dollar organizing effort in the months leading up to Election Day.

“The proof is in the pudding,” said Brad Dayspring, spokesman for the National Republican Senatorial Committee. “By any objective measure, they failed.”

Democratic party leaders and allied groups argued that the massive efforts they made to get voters out had a positive effect despite their losses. They pointed to boosts in the Democratic share of the electorate in New Hampshire and Colorado, as well as increased midterm turnout among African Americans in states such as North Carolina.

“We saw a real difference in turnout” in areas where Democrats invested resources, said Guy Cecil, executive director of the Democratic Senatorial Campaign Committee.

But he acknowledged that was “cold comfort,” given the party’s loss of the Senate. “I think this election was beyond turnout,” he said. “A good field program can make the difference of one, two, three percent . . . but when you are dealing with an election where independent and undecided voters move, it’s not sufficient.”

Voter participation nationally hovered at an estimated 37 percent — the lowest since 1942 — in large part because of low turnout in states such as California that did not have competitive statewide races. But the intense field programs on both sides drove up turnout in states with competitive Senate and gubernatorial contests, experts said.

In most of those places, “turnout was much higher, in some cases even 50 percent,” said Michael P. McDonald, an associate professor of political science at the University of Florida who tracks election statistics.

One exception was Virginia, where only about 37 percent of voters showed up at the polls. Neither party spent much in the state because neither expected a close race between Republican Ed Gillespie and Sen. Mark R. Warner (D), who ended up barely ahead.

The midterms posed a particular challenge for Democrats, who have come to rely on the young, diverse coalition that rallied around President Obama in his two White House races. Turning them out in an off-year election proved to be too great a task.

“The president is leader of a coalition of people who voted when he was on the ballot,” White House press secretary Josh Earnest said Thursday, noting that those voters did not turn out in full force this time. “So the question is, you know, what can Democrats do moving forward?”

The problem this year, according to Democrats and their allies, was that they could not overcome a sour national mood and a large wave of independent voters that broke for the GOP in the final weeks.

“I think where progressives locked in and invested heavily on the ground, we reached our goals, but it was not enough to compete with the tough political environment and losses among swing voters,” said Greg Speed, president of America Votes, which coordinates the efforts of independent groups on the left.

Republican strategists countered that their ground game was far more effective than the Democratic push, saying it made a crucial difference in tight Senates races such as North Carolina’s and Iowa’s.

A program coordinated by the Republican National Committee resulted in 35 million voter contacts that emphasized high-quality, in-person interactions, party officials said. In at least 11 states, GOP turnout was higher than it was two years ago.

“I can tell you one week when Guy Cecil said they knocked 140,000 doors, and that was their best week — well we did 268 [thousand] that week,” said Ward Baker, the NRSC’s political director.

The GOP Senate committee also tried to boost turnout at the margins in big cities where Democrats tend to dominate, not just in rural and suburban areas, Baker said.

Republicans were aided further by independent conservative groups such as Americans for Prosperity, which put tens of millions of dollars into its own program to reach voters in 19 states.

On the left, the Democratic senatorial committee poured more than $60 million into an 11-state program it dubbed the “Bannock Street” project, which harnessed 80,000 volunteers nationally who knocked on more than 10.2 million doors.

Party strategists said they saw evidence of the program’s impact in places such as Colorado, where GOP turnout beat Democratic turnout by nearly seven percentage points in 2010. This year, Democrats said, the Republican edge narrowed to five points in initial ballot returns and is expected to shrink further when all votes are tallied.

Despite that, Republican Cory Gardner beat Democratic incumbent U.S. Sen. Mark Udall. Cecil, of the Democratic senatorial committee, said the loss was due to the large number of independents who backed the GOP candidate. Democratic Party operatives also believe their turnout efforts helped Gov. John Hickenlooper (D) fend off a challenge from Republican Bob Beauprez.

In New Hampshire, Democrats believe canvassing efforts on the left helped save Sen. Jeanne Shaheen (D). Exit polls showed the state’s electorate was four percentage points more Democratic on Tuesday than in 2010.

In North Carolina — where 2.92 million voters cast ballots, a record for a midterm election — African Americans expanded their share of the electorate by two points over their 2010 figure, according to exit polls. Turnout in the largest Democratic counties, Wake and Mecklenberg, was up 16 percent over 2010, compared with 7 percent statewide.

Even so, U.S. Sen. Kay Hagan (D) was beaten by state representative Thom Tillis (R).

Cecil said he has no regrets that the party devoted so much money to its ground effort, saying the results underscored the need to operate permanent field programs.

“The only thing that would be disappointing to me would be if Democrats learned the wrong lesson — that we shouldn’t be investing in knocking on doors and calling our neighbors and asking people to turn out,” Cecil said. “We can’t wait until the midterms approach to invest in these states.”

Juliet Eilperin contributed to this report.