Mitch McConnell is closer to his goal of becoming Senate majority leader.J. Scott Applewhite/AP

It's looking more and more like Tuesday is going to be a big Republican night.

With most late polls breaking the GOP's way, Democrats would need multiple surprising victories in red states to keep control of the Senate for the final two years of the Obama presidency. Republican candidates in Iowa and Colorado have opened up small but consistent leads in the polling averages, while a strong Democratic challenger in GOP-held Georgia, Michelle Nunn, appears to be falling behind Republican businessman David Perdue in the campaign's closing days.

Republicans need a net gain of six seats to capture the majority, and Democrats have all but conceded losses in West Virginia, Montana, and South Dakota. Senator Mark Pryor of Arkansas has fallen significantly behind Republican Tom Cotton, while the would-be Republican majority leader, Mitch McConnell, now seems a near lock to keep his seat in Kentucky despite an aggressive Democratic push. The Democrats' only other shot at a Republican seat is in Kansas, while the GOP is eyeing pick-ups in Alaska, North Carolina, New Hampshire, and Louisiana, all of which remain close heading into Election Day. The red-tinted map means that Democrats would lose seats even in their best-case scenario, while Republicans could net as many as 12 if they sweep the competitive states.

Republicans were so confident over the weekend that a senior party official informed McConnell that he would indeed become the majority leader, The New York Times reported.

While Republicans have the decided advantage, the polls remain close in enough states to give Democrats a narrow path to the majority. In Alaska, for example, Senator Mark Begich's bid for a second term appeared in grave jeopardy for a time, but polls suggest his race against Republican Dan Sullivan has tightened up, and close campaigns in that sparsely-populated state are notoriously hard to poll and thus are impossible to predict. And a victory by Greg Orman over longtime GOP Senator Pat Roberts in Kansas could give Democrats an extra cushion, but only if the independent Orman decides to caucus with them in the Senate. Democrats are hoping their vaunted turnout operation will save Senator Mark Udall in Colorado as well as Bruce Braley, a congressman trying to win an open seat in Iowa.

Barring a Democratic upset, however, the biggest question come Tuesday is whether either party will have a clear majority by Wednesday morning. In Georgia and Louisiana, the leading candidate must earn more than 50 percent of the vote on Election Day to avoid a run-off election, and none of the contenders have topped that threshold in recent polls. The Louisiana run-off, likely between Democratic incumbent Mary Landrieu and Republican Bill Cassidy, would occur in December, while the run-off between Nunn and Perdue would not take place until January. The Georgia scenario raises the possibility that the 114th Congress will convene on January 3 with neither party holding a majority in the Senate, at least until the run-off on January 6. Run-offs in the two Southern states would also make them the center of the political universe for the next two months and add a new electoral dynamic to the decisions that a lame-duck Congress will make over the next several weeks.

There is much less suspense in the House, where Republicans are widely expected to pad their majority. Democrats have shifted their resources to protecting their own incumbents and are trying to hold GOP gains to the low single digits. But the GOP has expanded the map in recent weeks, leading the chief of the Democratic Congressional Campaign Committee, to describe the political environment heading into the election as "grim." The GOP goal is a net gain of 11 seats, which would give them 245 and the largest Republican total since in 1940s.

For Democrats, the imperative is to not let the House get too far away. The party is banking on a much more favorable environment during the presidential year of 2016, when many leaders hope to have Hillary Clinton at the top of their ticket. But with redistricting already narrowing the field, another GOP wave could put the chamber out of reach.

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