Sen. Kay Hagan (D-N.C.), left, and Libertarian Party candidate Sean Haugh, center, listen as Republican candidate Thom Tillis speaks during a debate at WECT studios in Wilmington, N.C., on Oct. 9. (Gerry Broome/Associated Press)

Thom Tillis sent a deep sigh and a shudder rolling through the crowd of Republican activists with just one word: ­“Ebola.”

“Can we all agree that it would make sense temporarily to have a travel ban?” the Republican Senate candidate asked about 100 supporters gathered Saturday afternoon at the local GOP headquarters in Guilford County. The crowd burst into hearty applause.

The specter of Ebola in the United States, on the heels of stories about the violent militants of the Islamic State, has made security a late-breaking wild-card issue in North Carolina’s Senate race.

For much of the year, the incumbent, Sen. Kay Hagan (D), and her allies had successfully framed the campaign as a referendum on the sharp conservative turn taken by the state legislature under the leadership of Tillis, the House speaker. But in the past few weeks, the conversation has pivoted amid alarming headlines about terrorism and a virulent epidemic, further tightening what is expected to be the most expensive Senate race in U.S. history.

Tillis has latched onto criticism of President Obama’s handling of the crises and sought to connect them to Hagan, part of his campaign’s broader aim to turn the race into a vote on the Democratic administration.

Sen. Kay Hagan (D-N.C.) makes a point while participating in a debate with Republican candidate Thom Tillis at UNC-TV studios in Research Triangle Park, N.C., on Oct. 7. (Gerry Broome/Associated Press)

“This president has failed the American people,” he told volunteers in Raleigh on Saturday. “Senator Hagan has been with him, with her rubber stamp, every step of the way. Our safety and security is more threatened now than it has ever been.”

Hagan has found herself on the defensive, acknowledging that she missed a classified briefing about national security threats to attend a campaign fundraiser in New York in February. On Friday, she called on Obama to temporarily ban the travel of non-U.S. citizens from affected countries in West Africa, just days after saying that such a tactic “is not going to help” unless it was part of a broader strategy.

Hagan’s campaign rejected the charge that she has not been engaged on security issues, noting that she has met with top generals in Afghanistan and Iraq and has chaired 20 meetings of a Senate subcommittee on emerging threats.

“Speaker Tillis can only criticize,” Hagan told reporters after a campaign stop in Charlotte on Sunday. “He has not one idea on his own that he would put forward — not one.”

The changed dynamic has lifted the hopes of national Republicans, who are pumping millions of dollars into new attack ads in the state amid signs that Hagan’s slight but steady lead has narrowed.

“Eyes are now starting to turn to Washington, and that’s probably the worst-case scenario for them right now,” said Paul Shumaker, Tillis’s campaign strategist.

“The president has done a good job of helping refocus this race for us,” Shumaker said, adding: “Thank you, Mr. President.”

House Speaker Thom Tillis talks to lawmakers on the House floor as the House and Senate re-convened at the General Assembly in Raleigh, N.C., in September 2013. (Gerry Broome/Associated Press)

But Democrats in the state are skeptical that the new story line will alter the views of what is a deeply polarized electorate.

“I think in the last week they have probably had a little headway in making it a nationalized election,” said Morgan Jackson, a longtime Democratic strategist in Raleigh. “The question is, is it too little and too late? If this was a month ago, it would be a much different situation. But the ability to change voters’ minds, that window is about to close.”

Allies argue that Hagan maintains key tactical strengths heading into the final two weeks of the campaign, in the air and on the ground.

Even with new infusions of cash from the National Republican Senatorial Committee and conservative groups such as the Koch-backed Freedom Partners Action Fund, Tillis and his backers are still outgunned on television by Hagan and her supporters, according to people familiar with ad reservations. That is particularly true in smaller markets such as Asheville.

At the same time, the Democratic incumbent is being bolstered by two ambitious field operations: one run by the party and the other driven by well-funded interest groups such as Planned Parenthood, the League of Conservation Voters and unions, coordinated by the liberal group America Votes.

“There’s no question that 95 percent of the voters have made up their minds,” said Rep. David E. Price, a Democrat who represents the vote-rich Research Triangle. “The real game is turnout.”

A stop Tillis made at the state fair in Raleigh on Friday underscored the visceral impressions that voters have about the candidates.

On one hand, there were people such as Scott and Alyson Dunlap of Statesville, who greeted Tillis with ebullience. “You’ve got my vote!” Scott Dunlap declared as they encountered him in front of a display of giant pumpkins.

“We’re conservative, so we’d like to get more conservative voices in Washington,” the 59-year-old IT director said afterward.

But outside a tobacco-curing demonstration, Virginia and Jerry Wall of Clayton responded with disgust when they heard the GOP candidate was nearby.

“I can’t stand Tillis,” said Virginia Wall, 68, a retired nurse.

“I’m a Republican, but I fear the direction the Republican Party has gone,” said her husband, a 64-year-old network engineer. “This voter-ID law they passed here in North Carolina, it borders on treason. It’s not what I expect from America.”

Hagan has sought to stoke that backlash against Raleigh’s conservative tilt. On Sunday, she stood in front of a big sign declaring “NORTH CAROLINA FIRST,” speaking to a clutch of students and educators at Charlotte’s Central Piedmont Community College.

She hammered Tillis on his education record, noting that the 2013 tax cuts passed by the GOP-led state legislature led to decreased revenues for schools.

“Y’all, we didn’t become the state we are by selling our students short,” she said.

On the campaign trail Saturday, Tillis rejected such critiques, pointing to teacher raises passed in the most recent legislative session.

For his part, he spent most of his day-long swing through the state pressing the argument that Hagan operates as an extension of Obama. He ticked off a series of issues, such as Obamacare and veterans’ care, in which he said the administration — and the senator — had failed. At every stop, he added two new items on the list: the Islamic State and Ebola.

“I don’t know about you all, but I pretty much had a sense that ISIS was a threat,” he told backers crowded in a field office in Cornelius, just north of Charlotte. “Senator Hagan decided that a Park Avenue fundraiser was more important than a classified briefing on ISIS,” he added, using another name for the Islamic State.

On Ebola, Tillis said, “Senator Hagan finally said that there should be a limited ban on travel from western Africa. Well, welcome to the club of common sense. But it’s not enough. This is an opportunity where she could have proven to be independent and say, ‘Mr. President, we need to protect the safety and security of America.’ ”

Hagan vigorously disputed his characterizations, saying Tillis had ducked questions about how he would handle the Islamic State.

“I support the airstrikes,” she said Sunday, adding that she called for moderate Syrian rebels to be armed and trained “a year and a half ago.”

As for her position on a travel ban, “nothing has changed, and Speaker Tillis knows that,” Hagan said. “He is trying to distract from what the truth is. I have always said that a travel ban should be part of a broader use of tactics.”

Whether there are any voters left to win over remains an open question. Nearly $80 million in political ads have already inundated the state, a figure that could rise as high as $100 million by Election Day.

“I would argue that persuadable voters are like pink unicorns,” Jackson said. “They are impossible to find.”

Ann Inman, a retired nurse who attended Tillis’s rally in Greensboro, said she was deeply concerned that the Centers for Disease Control and Prevention had “fallen down on the job” handling the arrival of Ebola in the United States.

But she was not sure that issue would sway many voters.

“I don’t think it has anything to do with the senatorial race,” the 68-year-old said.

Inman’s friend Sandra Burns disagreed.

“If she didn’t want to stop the flights coming in, she was with Obama on that!” said Burns, 72. “So if I was a Democrat and voting, I would think, ‘Hey, wait a minute here!’ ”

“I don’t know,” Inman mused. “I don’t know.”

In an interview, Tillis said he believes recent crises resonate because they “are very real examples for people to understand what it means for this president to fail on foreign policy.”

“I still think, though, that jobs and the economy are still top of mind,” he added. “It’s just these other issues have entered into the narrative in a much more prominent way than we expected them to.”