The short version is... it's doable.
I'm using this map to do the calculations, by the way: it's already adjusted DE & NH to Likely Democrat and Tossup, respectively (which looks accurate to me, although the latter at least is volatile and speculative).
- We start at 41.
- First wave is everything of ours legitimately at risk (FL, KY, LA, MO, NC, NH, OH). Just to be on the safe side, subtract NH, for the time being and until new polling comes out reflecting the new situation (PPP's does not actually tell you what the poll numbers were). The rest are reasonably safe at the moment. Net 40.
- Second wave is our more or less guaranteed pickups (AR, IN, ND). Net 43.
- Third wave is races where it's reasonable to bet that we're going to pick up seats (PA). Net 44.
- Fourth wave is toss-up territory (CO, IL, NV). We absolutely must get all three; NV is the riskiest, but Angle's still in there and messing up Reid's day. Assuming all three, Net 47.
- Fifth wave is where this gets hairy (CA, CT, WA, WI, WV). We'll need four of those to hit 51. Of them: CA, WA, & WI look fairly good right now, but the Democrats will firewall those states, if they firewall no others. CT's McMahon has a good campaign team and lots of money, and she needs both. WV's Manchin is surprisingly weak in his Senate bid, but he's got home-field advantage.
Conclusions? ...Well, it's going to be easy to get to 46. Deceptively not-impossible to get to 48. 51 is going to be hard. The good news is that NH may not actually be affected by whatever changes take place, which will make the fifth wave a heck of a lot easier to deal with: three of five is better than four of five. But note that even then I have to assume a sweep of the fourth wave in order to get to the fifth. I also have some slightly annoyed things to say about the state of the NY-SEN races, but we'll let that slide for the moment.