Republicans appear to hold a slight edge in the battle next year to control the Senate. But the wild swings in the political fortunes for both parties in the closing months of 2013 made clear the situation could drastically change.

“The playing field is currently tilted toward Republicans,” Jennifer Duffy, of the nonpartisan Cook Political Report, observes in her recent forecast, with several moderate Democrats in serious danger of losing re-election.

Such a scenario seemed hard to imagine in late summer when Tea Party-backed Texas Sen. Ted Cruz barnstormed the country to rally support for the essentially impossible task of “defunding” ObamaCare.

However, Republicans’ standing among voters appeared to take an even bigger turn for the worse when Cruz returned to Capitol Hill and led the party’s most conservative wing in a failed effort to shut down the government unless Congress defunded President Obama’s signature health care law.

"There's a belief that getting the [Senate] majority in 2014 is possible and we don't want to go down roads that make it harder," South Carolina Republican Sen. Lindsey Graham said at the time, adding the Cruz-led tactic was “a bridge too far.”

Yet just days after the government shut down then reopened, the ObamaCare website opened for business Oct. 1 to disastrous consequences, this time turning the political fortunes on congressional Democrats who supported the law.

A CNN poll released this week showed 49 percent of those surveyed now want to be represented in Congress by a Republican and 44 percent want a Democrat, compared to a poll in October that showed 50 percent wanted a Democrat and 42 percent wanted a Republican.

“This doesn’t mean, though, that there aren’t a number of questions that need to be answered between now and Election Day,” Duffy said about the current state of play.

Democratic strategist David Heller, president of Main Street Communications, points out that Capitol Hill negotiations over the debt ceiling are just around the bend. And if the GOP’s conservative wing is unyielding about cuts, voters will blame the entire Republican Party like they largely did in October when the debt negotiations almost sent the country over the fiscal cliff, he said.

“This is going to be very difficult for the Tea Party,” Heller told FoxNews.com. “To put at risk the full faith and credit of the United States is a serious thing to do. The pendulum could swing the other way.”

Right now, Democrats have a 55-45 majority with Republicans needing a net gain of six seats to take control of the upper chamber.

The Rothenberg Political Report -- another well-respected and non-partisan polling firm, predicts Republicans are likely to gain four to seven seats.

Nine of the 11 most competitive races are in states that Republican presidential nominee Mitt Romney won in 2012, and seven of those seats are held by Democrats, according to Cook.

However, while the election numbers are in Republicans’ favor, and Democrats appear to be hurting their own cause, the GOP has its own challenges.

Duffy points out some Republicans incumbents are facing tough primary challenges from the right, which in more recent elections has resulted in winners “too conservative to win the general election,” she argues.

Meanwhile, Democrats have recruited solid challengers in Kentucky and Georgia -- where the party has its best chances of winning Republican-held seats.

If Senate Minority Leader Mitch McConnell, a powerful fundraiser and campaigner, wins his primary challenge against Tea Party-back challenger Matt Bevin, McConnell will likely face Democrat and Kentucky Secretary of State Alison Grimes.

A poll release this month by the Democrat-leaning Public Policy Polling has McConnell with 43 percent of the vote, compared to 42 percent for Grimes.

In Georgia, the general election race for the seat of retiring GOP Sen. Saxby Chambliss will likely be Democratic candidate Michelle Nunn, a former nonprofit executive whose father is retired Democratic Sen. Sam Nunn, against the winner of the Republican primary that right now is a large, wide-open field.

Most eyes will also be on Sens. Mark Begich in Alaska, Mark Pryor in Arkansas, Mary Landrieu in Louisiana, and Kay Hagan in North Carolina --- Democratic incumbents being targeted by Washington Republicans.

“There’s danger lurking out there,” says the narrator in a Republican National Senatorial Committee ad aimed at Landrieu as an alligator skims across what appears to be Arkansas swampland.

The 30-second ad by the RNSC, which like the Democratic Senatorial Campaign Committee is expected to spend large sums in 2016, argues Landrieu cast a deciding vote for the passage of ObamaCare and continues to support law, though roughly 80,000 residents are expecting to receive health insurance cancellation notices this year.





