Democratic U.S. Sen. Al Franken, left, and Republican challenger Mike McFadden enjoy a laugh before their debate, Wednesday, Oct. 1, 2014, in Duluth, Minn. (Jim Mone/AP)

Republicans are bullish that they will win control of the Senate, make small gains in the House and retain many governor’s offices this year. But just over two weeks from Election Day, fears about Ebola and Islamic State militants, along with sudden, surprising scrambles in key states, have added new volatility to the 2014 campaign.

The political climate clearly favors Republicans, buoyed by President Obama’s record-low popularity and a voter-enthusiasm advantage. However, the kind of wave that lifted Republicans in 1994 and 2010 has eluded them, in part because the GOP brand also is damaged.

Voters are restive and dissatisfied with their political leadership, turning what had been a workmanlike slog of a midterm campaign into an unpredictable sprint. More sitting governors and lawmakers are in danger of losing today than just a month ago, while both parties see new opportunities and hazards, especially in the battle for the Senate.

“A lot of pressure is building up,” said Alex Castellanos, a veteran Republican strategist. “The top comes off the pressure cooker on November 4th and — boom! Democrats could surprise in some places and Republicans in others.”

Republicans have little margin for error as they seek the six seats needed to give them the Senate majority. The GOP’s fortunes have improved slightly in a trio of conservative-leaning states with embattled Democratic incumbents — Alaska, Arkansas and Louisiana — and it is expected to pick up Democratic-held seats in Montana and West Virginia.

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However, Kansas and South Dakota — races Republicans were expected to easily win — are now in jeopardy. Meanwhile, Democrats are gaining in Georgia and have a slim edge in North Carolina. Both parties see Colorado and Iowa as tossups that could determine the majority.

Worries over Ebola are further complicating candidate strategies. Many Republicans and some Democrats have called for travel restrictions on flights from West Africa, an idea opposed by the Obama administration and many public-health experts. In Iowa, the first questions at Thursday night’s Senate debate were about Ebola. In Minnesota, Mike McFadden (R) — the underdog challenger to Sen. Al Franken (D) — revamped his stump speech last week to capi­tal­ize on Ebola fears.

“The number-one role of the federal government is to protect our citizens,” McFadden told about 30 voters huddled in a Mankato sports bar Friday morning. In an interview afterward, he said: “It is the number-one question that I’m receiving on the trail. People are scared.”

All year, Republicans have tried to frame the election around Obama, attacking his health-care law in particular. Ebola, along with the rise of the Islamic State extremist group in Iraq and Syria, has offered the GOP a fresh entry point for criticizing the president’s leadership.

Brad Dayspring, the National Republican Senatorial Committee’s communications director, said of the U.S. Ebola response, “Obama is chasing it rather than leading it, and that adds to the concern that the federal government is slow and inept and at certain times incompetent.” Ebola, he said, has “intensified voters’ angst. It adds to the feeling of . . . ‘What is going on in that town?’ ”

Still, said Stuart Rothenberg, a leading handicapper, “there are some crosscurrents here. The national environment should favor Republicans up and down the ballot, but it’s not that clean.”

Republican and Democratic leaders are bracing for an inconclusive outcome if no candidate in Georgia or Louisiana finishes with more than 50 percent of the vote, which would force run-off elections in those states.

Little affection for Republicans or Democrats heading into midterms

Rob Collins, the NRSC’s executive director, confidently predicted in a briefing with reporters Thursday that the GOP would clinch the Senate majority on election night. Asked what will happen if Democrats defy the odds to hold the Senate, Collins joked, “I’ll be in an unmarked grave in Kentucky.” That’s the home state of Senate Minority Leader Mitch McConnell (R), who is favored in his reelection race against Alison Lundergan Grimes (D).

Democrats have invested heavily in their voter turnout organizations and believe that can give them a one-to-three-point advantage.

“Democrats are in position and are competitive in deep-red states,” said Matt Canter, deputy executive director of the Democratic Senatorial Campaign Committee. “We believe that if we’re competitive going into Election Day, particularly in smaller states like Arkansas and Alaska, the organization we have on the ground can win it for us.”

A deluge of money has rained down on key battlegrounds — much of it from outside groups whose donors are not disclosed — to fund a long and steady barrage of mostly negative television advertisements.

North Carolina’s Senate contest alone has drawn at least $55.7 million in outside spending, a record for a congressional race.

Thom Tillis, the GOP nominee, spent a warm Friday morning at the North Carolina State Fair in Raleigh, touring the fairway and glad-handing voters as the smell of funnel cakes and barbecued turkey legs wafted through the air. But the mood among voters was not quite so ebullient.

“There’s a lot of mudslinging going on,” said Tillis supporter Doug Boyd, a 49-year-old farmer.

“It’s nasty,” agreed Virginia Wall, a 68-year-old retired nurse who is backing the incumbent, Democrat Kay Hagan.

Despite the heavy spending, polls have shown relatively little movement in North Carolina and most other targeted Senate races.

“I’ve never seen anything so stable,” Democratic pollster Stan Greenberg said. “You expect in an off-year it would break for somebody in the end, but these races are not breaking.”

There has been unexpected movement in a trio of states, however. In Kansas, Sen. Pat Roberts (R) faces a tough challenge from independent businessman Greg Orman, while a three-way race in South Dakota has become competitive after an immigration investment scandal weakened former governor Mike Rounds (R). And in Georgia, David Perdue (R) has come under fire from Michelle Nunn (D) over his outsourcing of jobs as a businessman.

Demonstrating the growing importance of the Georgia race, Sen. John McCain (R-Ariz.) swooped in Wednesday to campaign with Perdue at a Veterans of Foreign Wars hall in Marietta. He joked about Congress’s dismal popularity ratings.

“Is there anyone here who’s in the 12 percent who approves of Congress?” McCain asked. “If you are out there, I’d like to know where the hell you’ve been. We’re down to paid staff and blood relatives. I’m not making this up, now. My mother is 102 years old. I received a phone call the other day from my mother — we’re down to paid staff.”

Obama’s approval rating fell to a record low of 40 percent last week in a Washington Post-ABC News poll that also showed an enthusiasm advantage for the GOP — 77 percent of Republicans said they were certain to vote, compared with 63 percent of Democrats. But while more than 6 in 10 Americans said the president lacks a clear plan for governing, a slightly higher percentage said the same about Republicans in Congress.

Former president Bill Clinton, who is stumping for Democrats nationwide, said in New Hampshire on Thursday that the electorate is jittery. “People are unsettled, but they’re not buying what the other guys are selling,” Clinton said, arguing that “it is not 2010 — and it is not 1994.”

Underscoring the uncertainty, governor’s races have tightened in unexpected places because of state-specific issues or poorly performing candidates. Republican incumbents in Alaska, Georgia, Kansas and Idaho are locked in closer races than anticipated, while Democrats face head winds in usually reliably blue states such as Connecticut, Massachusetts and Oregon.

Much of the focus is on the reelection campaigns of three prominent Republican governors — Scott Walker of Wisconsin, Rick Scott of Florida and Rick Snyder of Michigan. Polls show that Snyder has slight advantage, but the Florida and Wisconsin contests are tight. Scott may have hurt himself at a debate Wednesday when he delayed walking on the stage, in protest over Charlie Crist, his Democratic challenger, using a small fan under his podium.

The nation’s most vulnerable incumbent is Pennsylvania Gov. Tom Corbett (R), who appears headed toward defeat against Tom Wolf (D). But another endangered governor, Pat Quinn (D) of Illinois, has rebounded this fall, and recent polls give him an edge.

Almost certain to retain their House majority, Republicans are making a late, aggressive push into some solidly Democratic districts, including in California, New York and New England — all places where Speaker John A. Boehner (R-Ohio) has been campaigning.

Democratic leaders acknowledge the bleak landscape. The party has shifted its advertising buys to reinforce vulnerable incumbents — including Reps. Brad Schneider (Ill.), William Enyart (Ill.), Rick Nolan (Minn.), Sean Patrick Maloney (N.Y.) and Ami Bera (Calif.) — and has abandoned challengers in Republican-controlled districts.

Castellanos, the strategist, said of the GOP outlook: “There’s a wave, but there’s a wall. . . . Government’s failing. Nothing works. People are trapped in a room with President Obama and the Democratic Party, and there is a huge demand for change. They want to get out of that room. But the only door out leads to a room full of lepers — that’s the Republican Party.”

Anne Gearan in Manchester, N.H.; Matea Gold in Raleigh, N.C.; Paul Kane in Mankato, Minn.; Ed O’Keefe in Marietta, Ga.; and Jose DelReal and Sean Sullivan in Washington contributed to this report.