Six-term Sen. Thad Cochran and tea party candidate Chris McDaniel are making their final pushes today in the Magnolia State. The Post's Robert Costa and Jeff Simon are on the ground and report. (Jeff Simon/The Washington Post)

Republican Senate candidates Thad Cochran and Chris McDaniel returned to core campaign themes ahead of a Tuesday runoff election as GOP leaders nervously looked on, unsure of who would win and worried that the spectacle of Mississippi politics has become a national headache for the party.

As he greeted diners Monday at Jean’s Restaurant, McDaniel dismissed the anxiety of his party’s elders and confidently predicted that he would topple Cochran, a titan of Mississippi politics who was first elected to the Senate in 1978.

McDaniel, a 41-year-old state senator, compared his populist insurgency to that of David Brat, a Republican who defeated House Majority Leader Eric Cantor (R-Va.) in a primary earlier this month.

“People are ready for change in Washington, and Virginia was good evidence of that,” McDaniel told reporters. “We’re going to make Mississippi the center of the nation tomorrow.”

Cochran, meanwhile, stumped at a war memorial in Jackson on Monday with Sen. John McCain (R-Ariz.), a prominent voice on foreign policy and a fellow Navy veteran. The event underscored the 76-year-old Cochran’s hawkish worldview and his years of procuring federal funding for the state’s military bases.

McCain, a former prisoner of war in Vietnam, talked up Cochran’s character and called him a “good and decent and honorable senator.”

In its final days, the race has become a bitter and ugly contest with relatively little attention paid to the policy differences between the two candidates. Instead, there has been name-calling on social media, racial tension and warnings about voter fraud from McDaniel supporters, who sense a tea party victory but fear that Cochran — with the backing of some Democrats — could survive.

The controversies are the latest in a campaign dominated by them, including four arrests last month after a McDaniel supporter took a picture of Cochran’s wife, Rose, who is in a nursing home.

On Sunday, the Cochran family again became a topic when the McDaniel campaign criticized Katherine Cochran — the incumbent’s daughter and a college professor — in response to a Facebook posting she published last week. In that missive, she called McDaniel’s campaign an effort “engineered to appeal to the very worst in our electorate.”

In its mocking rebuttal on Facebook, McDaniel’s campaign used the hashtag “Who’sYaDaddy?” under a black-and-white picture of her, drawing an angry response from Cochran’s spokesman, Jordan Russell, who called the phrase “appalling” and “further proof that [McDaniel] is unfit for office.”

Meanwhile, right-wing activists and national conservative groups, such as the Senate Conservatives Fund and the Tea Party Patriots, are pouring into Mississippi to look for alleged voter fraud. Since the state does not register by party, the activists say that Cochran’s outreach to Democrats — emphasizing his record of securing federal funds for state schools and social programs — could tilt the election.

Cochran’s allies said the poll watching is a thinly veiled attempt to intimidate voters, especially black Democrats, in a state with a history of racial division.

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When asked whether he approves of the highly organized push to observe polling locations, McDaniel smiled and said he “absolutely” did. “To the extent that they can assist in finding fair elections for Mississippians, we’re all for it,” he said.

Inside Jean’s, Annie Stewart, a black medical worker who watched McDaniel shake hands as she ate lunch, said she was growing increasingly wary of his politics and the way the race has unfolded. “Sometimes, I wonder what’s actually going on here,” she said. “It’s gotten so negative.”

Jamie Johnson, an employee of the restaurant, said he also felt uneasy about the deeply personal nature of the primary. “The shadiness of it is something I’ve thought about a lot,” he said. “You know, just because we put McDaniel’s picture on the wall doesn’t mean he can count on my vote.”

A recent poll by Chism Strategies, a Democratic firm, showed McDaniel ahead by 52 percent to 44 percent among those who had voted in the June 3 primary. Cochran’s campaign said its internal data shows a “tight race.”

On Monday night, McDaniel was in Flowood, Miss., shaking hands with supporters and sounding upbeat about his chances after days spent canvassing the state with the Tea Party Express.

Cochran, however, is betting that Republican supporters, some of whom stayed home earlier this month, and sympathetic Democrats will help him win.

Flanking him in Jackson on Monday were powerful Mississippi Republicans, including Gov. Phil Bryant and Sen. Roger Wicker. They spoke urgently about the necessity of keeping Cochran, a senior member of the Senate, in office.

“Once I think it was Harry Truman who said, ‘if you want a friend in Washington, go out and buy a dog,’ ” McCain said. With Cochran, he added, “you have a friend in Washington and I have a friend in Washington.”

Jeff Simon contributed to this report.