Republicans were positioning themselves for a likely US Senate takeover after Tuesday's elections, but Americans may ultimately have to wait until December or even next year to learn who controls the chamber.
Recent polls show Republicans pulling ahead of President Barack Obama's Democrats in the battle for power in Washington, and despite states like Alaska and North Carolina remaining too close to call Monday, Republicans expressed confidence in the home stretch of one of the most consequential midterm elections in years.
"We intend to be a responsible governing majority if the American people give us a chance to do that," the Senate's top Republican Mitch McConnell told ABC News Monday in Kentucky.
The veteran politician has been locked in a tight race with resilient Democratic challenger Alison Lundergan Grimes, but two weekend polls show McConnell extending his lead.
A Senate flip would likely see McConnell as the new majority leader, something Republicans sounded increasingly bullish about.
"The wind is at our backs," Senator Rand Paul, a potential 2016 Republican presidential candidate, told CNN Sunday.
"I think people are ready for new leadership."
Republicans for months have hammered home their message that a vote for them is a vote against Obama.
"This is a referendum on the president," Paul told NBC.
Republicans already hold the House of Representatives, where all 435 seats are in play, and forecasters predict they will gain seats.
Three top forecasters now give Republicans between a 70 percent and 77 percent chance of winning the Senate.
But the full picture may not emerge on Tuesday. There are strong prospects for runoffs in Louisiana and Georgia, where rules require a second round if winners do not earn more than 50 percent of the vote, and a probable days-long ballot count in remote Alaska where there is an unpredictable and tight race.
Louisiana's runoff would be December 6, but a Georgia runoff would be January 6, three days after the new Congress sits in Washington.
Polls show that Republicans would have the advantage in both runoffs, although there would be an intense ground game and ad war in both states, especially if the fate of the Senate were still up in the air.
- Republican momentum -
In the heartland state of Iowa barely a day before polls open, the Des Moines Register put Republican Joni Ernst a full seven points ahead (51-44 percent) of congressman Bruce Braley, who is struggling to keep the Senate seat in Democratic hands.
Ernst, an Iraq war veteran, admitted Monday she was "very excited" about the poll.
"It just shows the momentum that we have here in Iowa," she told Fox News. "People are rejecting the failed policies of congressman Braley (and) they want a new direction for America."
Other data suggested the race was dead even. A Quinnipiac University poll released Monday showed Ernst and Braley were tied at 47 percent.
Democrats currently hold a 10-seat Senate advantage, 55-45. If Republicans take a net six seats they flip the chamber.
An incumbent president's party historically fares badly in elections in the middle of his second term, and this midterm is expected to be no different.
With Republican voters showing greater enthusiasm, Obama warned Democrats they could not afford to stay home.
"There is no excuse for us to just give away our power," Obama, whose poor approval ratings have largely kept him off the campaign trail, said at a rally Sunday in Philadelphia.
"You all have to vote. That's what this comes down to."
One Democratic casualty could be Senator Mark Udall of Colorado, a swing state where early ballots show challenger Cory Gardner with an eight-point advantage.
There are wildcards in the mix. Independent Greg Orman could oust Republican Senator Pat Roberts in Kansas, and he said he could caucus with Democrats or Republicans.
With trends not going their way, top Democrats including Vice President Joe Biden nonetheless put a brave face on the races.
"I don't agree with the oddsmakers. I predict we're going to keep the Senate," he insisted.
Asked whether Obama agreed with Biden, White House spokesman Josh Earnest said: "He does."
Yet Biden acknowledged the Republican potential.
"Quite frankly, going into 2016 when Republicans (have) to make a decision whether they're in control or not in control, are they going to begin to allow things to happen, or are they going to be obstructionists?" Biden told CNN. "I think they will choose to get things done."