Washington (CNN) -- The battle for control of Congress is entering a final, frantic five-day stretch that favors Republicans but has room for plenty of surprises that could determine which party will run the Senate.
The unsettled nature of so many individual contests at this late stage underscores the unpredictability of this election season. And Election Night could turn out to be a nail-biter that continues for days -- or even months.
The themes that were expected to dominate this election cycle -- Obamacare and immigration -- are turning out to be duds. Meanwhile, threats posed by Ebola and ISIS -- hardly dinner table conversations a year ago -- are suddenly top issues.
And on top of all that, add a mix of 2016 presidential drama as potential contenders barnstorm early voting states to help congressional candidates.
The GOP is poised to extend its grip on the House and needs a net gain of six seats to take back the Senate for the first time since 2007. Republicans are expected to easily take Democratic seats in Montana, South Dakota and West Virginia, leaving them needing just three more seats to build a Senate majority.
But getting there could get tricky.
North Carolina Democratic Sen. Kay Hagan is holding firm in a race many observers thought she would have lost by now, up four points in an Elon University survey over her challenger, Thom Tillis.
In Georgia, Democrats believe that Michelle Nunn — one of the emerging stars of this election cycle — could beat Republican David Perdue. If neither candidate gets 50 percent of the vote a run-off election will take place in January.
In Kansas, Senator Pat Roberts is still slugging it out against independent candidate Greg Orman and even the man most likely to become majority leader in a Republican Senate, Mitch McConnell, cannot take re-election for granted in Kentucky.
The loss of any of that trio would complicate Republican hopes in the Senate. Still, there are other pickup opportunities for Republicans.
In Colorado, Democratic Sen. Mark Udall seemed to be in good shape just a few months ago. But now he's down by seven points to Republican challenger Cory Gardner in a Thursday Quinnipiac University survey. The Denver Post had the race closer — with Gardner up two percent.
In New Hampshire, Democratic Sen. Jeanne Shaheen is in a very tight race with former Massachusetts Sen. Scott Brown. Meanwhile, Arkansas Democratic Sen. Mark Pryor, fighting an uphill battle in an increasingly red state, was down between 13 and seven points to challenger Tom Cotton in two recent surveys.
Other key states where Republicans have a good chance of picking up seats include Louisiana, Alaska and Iowa.
Though the 2014 race isn't even wrapped up yet, the next election in 2016 is already unfolding as potential presidential candidates stump in key early voting states.
New Jersey Gov. Chris Christie announced plans to blitz 19 states before Election Day, including Iowa, New Hampshire and South Carolina, which will play outsized roles in the presidential campaign. Jeb Bush, meanwhile, made waves by jabbing Hillary Clinton over her attitude towards business.
On the Democratic side, Clinton, who increasingly appears to be waging an undeclared presidential campaign, tracked through Iowa this week -- the state that did most to doom her 2008 White House bid.
Obama remained a sideshow, with his low approval rating making him unwanted by Democrats in swing states. So, he has been largely confined to raising millions of dollars for Democratic Party coffers, or stumping for candidates in liberal territory.
On Thursday, Obama was headed to Portland, Maine, to campaign for Rep. Mike Michaud who is seeking to unseat Republican incumbent Paul LePage in a tight governor's race.
CNN's Ashley Killough, Dan Merica and Jeremy Diamond contributed to this story