If members of the Obama team (and Democrats generally) think that the attacks coming from the Clinton team are harsh, then they are definitely not ready for prime time. If you want a foretaste of how nasty the general campaign will be, check this:
This video will have a million views by the weekend, and it captures the majority view of the GOP. (Moreover, viewed purely technically -- that is, as propaganda -- the video is undeniably brilliant.)
The question now is how Obama will respond. This is in the same vein as swift-boating and other calumnous attacks on the very strengths of a candidate: what such attacks really test is a candidate's ability to fight back. The nagging doubt all along about Obama has been his willingness to fight when called out.
The moment of course is tricky, since he's still in a primary battle with Hillary. But it's basically a campaign he's won by now, which means he should feel free (indeed obligated) to respond to this attack in force and with numbers. Hillary's side won't score innings by attacking his counterattack (unless, of course, his counterattack is ham-fisted--in which case Hillary is the least of his worries). What Obama need to realize is that to not respond will have even more dire consequences than whatever the backlash against the response.
it goes without saying, of course, that in this case Obama ought to "respond" through the usual proxies...