Some critics question whether the effort might lead to voter intimidation. The Mississippi NAACP dispatched about 250 volunteers to watch poll stations and look for any signs of interference.

They're supposed to call the state office if anyone is turned away, but enforcing the crossover primary rule may be hard to enforce.

Wayne McDaniels, president the NAACP's Jackson City Branch, said the biggest concern is polling stations in rural areas.

"There won't be much coverage as far as the news media out there, so those are the pockets where someone might figure they can get away with certain things," he said.

McDaniels said the state office hadn't yet receive any calls or suspicious reports from any of the volunteers in the field.

CNN saw three people turned away by poll workers in Jackson because they voted in the Democratic primary.

Monitoring crossover voters

Adams is overseeing the "election integrity project" for the conservative groups FreedomWorks, Tea Party Patriots and Senate Conservatives Fund, said Monday in a phone interview that volunteers won't be instructed to talk to voters or poll workers, but only monitor the process at polling stations across the state.

"These are not negotiators," he told CNN, stressing that they're "not activists urging people" to vote one way or the other.

He said the volunteers will "observe what's going on and how to memorialize the events of the day in an observer report," which will be reviewed by lawyers. But he refused to elaborate on who the lawyers are and who they work for.

He also declined to be more specific about where exactly the volunteers would be working, saying only that they will be stationed at polling locations "across the state." Pressed on why he was providing few details about an effort that seeks transparency and honesty in an election process, Adams didn't give an answer.

McDaniel, who chairs the elections committee in the state Senate, said Monday he approves of the monitoring effort and doubts intimidation will become an issue.

"The issue is to make sure we have a fair process," he said.

He argued that a high Democratic turnout for Cochran would reveal the senator's true colors.

"I'm not concerned about them being African-American. I'm concerned about them being liberal," he told CNN. "That's always been my concern. If Senator Cochran is going to court liberal Democrats to save his seat, that's a good indication that he's abandoned conservatism in Mississippi."

Learning from last time

Since Cochran failed to defeat McDaniel in the primary, the senator and his campaign have been more aggressive about their ground game.

Sources familiar with Cochran's campaign strategy say they hope that a lot of Republicans who stayed home during the primary, thinking Cochran would be fine, will show up at the polls.

The senator has had a more active schedule for the runoff and his overall operation is more finely tuned. On Monday, he campaigned with McCain, who reiterated the pitch that an experienced senator is more beneficial for a state.

McDaniel doubled down on his attack line against Cochran, saying his partnership with McCain further proves how out of touch the senator is with conservatives.

Former Sen. Lott has also helped out Cochran by cutting an ad for his former colleague. He said he didn't do much for Cochran in the primary because "I think they didn't think they needed me." But the runoff's been different.

The U.S. Chamber of Commerce also pitched in for Cochran and produced an ad featuring retired NFL star Brett Favre, a Mississippi native. But Cochran isn't the only one with a celebrity endorsement. Longtime game show host Chuck Woolery headlined a bus tour organized by the Tea Party Express.

While Cochran has tried to make the case that his near-four decades in the Senate brings wisdom and power, he's fighting an uphill battle against a younger politician and former talk radio host who paints himself as the candidate more principled and eager to help lead a conservative movement in the Senate.

Jeremiah Boddy, 20, a student at the University of Southern Mississippi and a McDaniel supporter, showed up to a Cochran event Monday.

"I feel like it's the same rhetoric, just washed and put in different clothes," he told CNN. "I mean he has no charisma, and as far as I'm concerned, he couldn't sell you a brand new car, even if it was free."