This is further evidence of a "groundswell", and that's very, very good news for the GOP.
Typically, modern Presidential campaigns begin with about 70% of the electorate already decided. Another 15% or so tend to follow in the weeks immediately following the nominating conventions. The final 15% does not "lock-in" until the three-to-four week period immediately prior to the election - "debate season", if you will.
The key takeaway from past experience is that once that final decision and lock-in occurs, it moves in one direction only and does not significantly change. Either the swing vote decides to stay with the incumbent or incumbent party, or moves to the challenger.
In 2008, the race was close until mid-October, when undecided voters moved decisively toward Obama. This year, the final movement has been in Mitt Romney's direction, and just as decisively. The remaining two Presidential debates might move some people, but they are unlikely to be as decisive as was the first debate.
The 15% of truly undecided voters saw Mitt Romney, many for the first time, unfiltered by either the opposition or the news media (insofar as a difference exists between them) and largely, they liked what they saw. Hence, the Obama campaign's frantic efforts to stuff the genie back in the bottle, or rather: to reconstruct the Straw Man Romney they had crafted and were running against, because the Real Romney proved so much more attractive to swing voters.
I will predict with some confidence that Obama and the Democrats will fail in the next three weeks to change those minds already made up. Because by now, most everyone has decided for whom to entrust the nation's future.