To begin with, we should acknowledge that a Republican takeover of the upper house is anything but a sure thing. The midterms are still seven and a half months away, and a lot could happen between now and then….
If the Republicans do take the Senate, they won’t have a lot of time to savor the victory, because two years later they’re going to be the ones defending more seats (see Sean Trende’s analysis for more details). That makes it entirely possible, maybe even likely, that Republicans will have control of both houses for only two years, and after 2016 we’ll go back to the way things are now. So can they legislate during that time?
To a certain degree, the question is moot as long as Obama is president. Anything big and consequential on the Republican agenda would get vetoed. But you can accomplish a lot by thinking relatively small. The question is whether Republicans — or to be more specific, House Republicans — are capable of doing that.