It's way too early to make midterm predictions.

I'm amused.  Nate Silver has gone all in on data crunching to show that Republicans are now slightly favored to retake the Senate.  The problem is, we haven't even reached primaries, so these numbers are meaningless.

I have briefly looked at RCP's data, and as far as I can tell there are three takeaways:

1. GOP pollsters are finding what they mostly want to find, while Democratic pollsters are mostly finding what they want.  Which is to say that both sides might be fooling themselves if they think they know where the races are headed.
2. If you look at the last three weeks of polling data, Democrats are doing mostly fine.
3. In some cases where a Republican candidate is polling ahead of the Democratic candidate, you will see that that individual is not the front-runner of the GOP primary poll.

So again, it's way too early to make predictions.  The races are extremely fluid with a lot of things going on between today and November.  The earliest one can do a proper prediction is post-May primary season.

Republicans really do believe that the ACA will doom Democrats.  I think they're wrong for three reasons:

1. Despite all of the ACA's troubles in implementation, the horror stories were generally false narratives with people offering politically-driven bias to their personal stories of doom.  When pushed and shown how the ACA had helped them, these same people remain adamant that they're right and everyone else is still wrong.  You can't help people suffering from the Dunning-Kruger Effect.
2. It's still the economy, stupid.  I'm sure that, were the US to have hit even a mini-recession in 2012, Democrats and President Obama would have had a much harder time winning.  For the rest of 2014, most all economic forecasting indicates continued strong growth in the US...that is, once we get past Winter in the east.  Nonetheless, dude, there are a dozen construction cranes within a 5-mile radius in Portland Oregon.  There is a point to why Janet Yellen signaled the probable increase in rates next year, and earlier this year, the continued reduction in QE.
3. Republicans are known to stick their foot in mouth and snatch defeat from the jaws of victory.  Trust me, the pull from the far-right continues unabated.