They’re sick of the noise and the fighting. They think this thing is wrapped up. They’re just not excited about the candidates.

Whatever the reason, Republican voters — and perhaps just people generally — seem to be losing interest in the party’s prolonged and messy contest to choose a nominee to challenge President Barack Obama in November.

Voter turnout in the 22 states that have held primaries and caucuses so far, including the 10 states that voted on Super Tuesday, has fallen about 8 percent overall compared with 2008. In seven of those states, the decline has been far more dramatic, with at least one in five voters staying away compared to the same primaries in 2008.

Television ratings for the Republican debates started strongly last year, suggesting that viewers were hungry to see the 2012 candidates in action. But the numbers for some campaign events have plateaued, too.

Primetime ratings for Super Tuesday coverage on the three leading cable news networks fell nearly 40 percent compared with the same coverage in 2008. And this time around, the broadcast networks — which had attracted some 15 million people to Super Tuesday coverage in 2008 — didn’t even bother to show it. Only NBC cut into its regular entertainment schedule, with just an hour-long show to cover the big vote.

Of course, it’s hard to compare any two election cycles since no two are entirely alike. The 2008 campaign may have been especially unusual, given that it featured an open race, and two Democratic front-runners — Barack Obama and Hillary Clinton — who inspired an extraordinarily passionate response from supporters.

But even with those caveats, the 2012 campaign is starting to drag for would-be voters and viewers.

“Something has turned them off,” says Chuck Todd, NBC News’ political director and chief White House correspondent. “Is it Limbaugh or the negativity or the super PACs? We don’t know fully why. But there’s something happening here.”

Or simply not enough happening to bring people out. The trick for Republicans, and perhaps for Obama, too, is going to be how to figure out how to avoid the same thing happening in November.

“I think we are going to have a … challenge” firing up the base, said Ken Blackwell, a Republican who has served as Cincinnati mayor and Ohio’s secretary of state. “And we need to start working on that right now.”

Low voter turnout tends to favor the party in power, but the relationship is by no means clearly established, said Michael McDonald, a political science professor at George Mason University. “It’s difficult to extrapolate from what we’re seeing here,” he said.

But Blackwell sees an evolutionary shift at work. There was once a greater emphasis on waging campaigns at the level of handshake-to-handshake, he said. But in the era of the Super PAC — in which nominally independent committees can raise and spend unlimited sums to support a candidate — campaigns are waged more than ever in the haze of negative TV advertising.

“Part of the base intensity problem is the direct result of the negative ads that are run by consultants,” said Blackwell, who chairs the Faith and Freedom Coalition of Ohio, an organization that promotes lower taxes and small government. And with the millions flowing into super PACs for both parties, Blackwell expects more of the same through general election this fall.

“There’s going to be more blood on the ground before flowers sprout out,” Blackwell said.

Another possible factor: Republicans haven’t seen a primary this long and this nasty in more than a generation. The 2012 campaign is out of step with a party culture that values order in its in-house battles, a system that has favored candidates who were next in line and had waited their turn: Ronald Reagan in 1980, George H. W. Bush in 1988, Bob Dole in 1996 and John McCain in 2008.

Disrupting that culture has been unsettling.

“Republicans are genetically predisposed to a less messy process,” said Terry Holt, a Washington-based media strategist who worked as a senior advisor on George W. Bush’s 2000 and 2004 presidential campaigns. “It goes against our nature to have a protracted battle. We have a tradition of validating the frontrunner and moving on to the general election.”

Holt thinks the up-and-down nature of the primary — the shuffling of front-runners and cannonades of criticism — could be taking a toll. And there’s “some measure of consternation” among the Republican establishment, Holt said. “Republican voters have seen such a mixed result that there may be some fatigue with the melodrama they’ve seen day-in-and-day-out.”

Todd thinks that could be a problem come November: “If I were a Republican strategist, I would be looking at the tone, the turnout and the poll numbers and I would worry that we have an enthusiasm problem, that we’re not going to get the kind of turnout we need for a change election.”

Holt, however, expects the fractured party to come together by November — and the Republican voters to come out again — for the simple reason that they’re united in the desire to chase Obama from the Oval Office.

“That fatigue will go away,” he said. “The anger and the anxiety is out there. It’s not going to go away just because the Republicans had a tough primary. Republican voters, older voters, national security voters — the kind of voters who vote in presidential elections — are the most reliable voters that we have year-in and year-out.”

Despite the volatility of the race, many Republican insiders expect former Massachusetts Gov. Mitt Romney to win the nomination. But that sense of inevitability may have been counter-productive, they say, leading some voters to ask, “Why bother?”

“In a lot of people’s minds — for good or for bad — they see this race as over,” said a young Republican activist who asked to remain anonymous in part because of his own lack of enthusiasm for Romney. On Tuesday night, he said he was feeling so blase about the primary returns that he made another choice: “I’m going to catch up on my DVR.”

So, apparently, did a lot of voters in his generation. Only 5 percent of eligible voters younger than 30 cast ballots on Super Tuesday, roughly splitting evenly between Romney, former Sen. Rick Santorum, R-Pa., and Rep. Ron Paul, R-Texas, according to an analysis by the Center for Information and Research on Civic Learning and Engagement at Tufts University.

So far, only about 600,000 voters younger than 30 have cast ballots in all the Republican primaries, said Peter Levine, CIRCLE’s director. That’s less than half the number who voted for then-candidate Obama prior to Super Tuesday in 2008, although that’s an imperfect comparison because there were more primaries before Super Tuesday in 2008.

But the difference is so large that it points to a big potential weakness, Levine said.

Finding a way to nudge more young Republicans away from the DVR and toward the voting booth might address some of the turnout problem. “It’s not an insoluble [problem]” Levine said. “This is under the category of, ‘They’ve got work to do.’”