Democrats currently hold a 55-45 majority in the Senate. Republicans need a net gain of six seats to win a majority there.
This looks to be within reach. Seven Democratic-held seats are up in states carried by Mitt Romney. And four Democratic incumbents are seeking re-election in target states in the 2012 presidential election.
In three Romney states -- Montana, West Virginia, South Dakota -- Democratic incumbents are retiring. The likely Republican nominees, two current House members and a former governor, have been leading by wide margins. These are not gimmes yet, but they probably will be.
Of the four incumbent Democrats running in Romney states, only one, Alaska's Mark Begich, has a statistically significant lead in the most recent public poll. But it was conducted in August.
A Republican poll last weekend in Arkansas found challenger Tom Cotton leading Mark Pryor 48-41. That's a significant difference from pre-Oct. 17 polling showing an even race -- and that's bad news for an incumbent.
In the first 10 polls, Hagan led controversial state House Speaker Thom Tillis by an average of 48 to 38 percent. In two polls conducted since the Obamacare rollout began, Hagan’s lead was down to a perilous 44 to 42 percent.
Races have been tightening in 2012 target states too. Colorado Democrat Mark Udall led 2010 Republican nominee Ken Buck 50-35 last June -- post-rollout, his leads were 45-42 and 46-42.
In 2012 Mitt Romney carried Colorado whites 54-44 but lost Hispanics 75-23. Given Barack Obama’s big post-rollout slide among Hispanics nationally, Udall may have difficulty matching Obama’s Hispanic numbers.
Democratic Rep. Bruce Braley has been the favorite to replace retiring Iowa Sen. Tom Harkin. But a Republican December poll showed Braley with only 40 to 42 percent support, and just 3 to 6 points ahead of five Republicans that have limited name recognition.
Pre-rollout polls showed New Hampshire incumbent Jeanne Shaheen with double-digit leads over state Republicans. But she led former Massachusetts Sen. Scott Brown by only 48-44, and Brown now seems interested in the race.
Obama carried Michigan 54-45 in 2012. But a Democratic poll this month shows Republican Terri Lynn Land leading Democrat Gary Peters 42-40. Neither is well-known. But the Republican label seems surprisingly strong in a state where Republicans have won just one Senate race in the last 40 years.
So Republicans have plausible chances to gain as many as 11 seats. But there are countervailing factors.
Republicans nominated some astonishingly weak candidates in winnable races in 2010 and 2012, and Democrats hope they will do so again in Georgia, where Michelle Nunn, daughter of former Democratic Sen. Sam Nunn, has been running roughly even with — or a bit ahead of — various Republicans.
And Democrats have hopes of depicting Senate Minority Leader Mitch McConnell as a Washington insider and toppling him in Kentucky, despite the state's anti-Obama leanings.
That being said, National Journal’s survey of Washington political insiders shows most Republicans and a near-majority of Democrats predicting a Republican Senate majority. That’s noteworthy, because these insiders, who spend so much time with incumbents, didn’t predict party takeovers in 2006 and 2010 at this point in those election cycles.
The Obamacare rollout has also shifted opinion on the generic vote — which party’s candidate do you support for the House of Representatives? When the shutdown ended, Democrats led 47-41 in Real Clear Politics' average of recent polls.
Now, Republicans lead 44-41 on the question that has often underesimated actual GOP performance. Analysts Stuart Rothenberg and Larry Sabato see more than 20 Democratic House seats at serious risk.
All this could change if public opinion on Obamacare — or Obama — shifts once again. But it looks like recent obituaries of the Republican Party were premature.