When did the conventional wisdom change?

It used to be the conventional wisdom that "Republicans are better for the economy." Now the pendulum have swung the other way, big time:

In Illinois' 13th district, an exurban Chicago seat where veteran Rep. Judy
Biggert (R) is running for re-election, Belcher found that voters trust
Democrats to fix the economy more than Republicans by a 19-point margin. They
gave Democrats a 15-point edge on energy issues and an 11-point advantage on the
broad question of which party "shares your values." And that's all in a district
where President Bush won by 10 points in 2004 and 13 points in 2000.

The story is similar in the neighboring 6th district of freshman Rep. Peter Roskam
(R). The seat has long leaned Republican -- Bush won it by 6 points in 2004 --
but now, Belcher found, Democrats have a 14-point edge on the economy and a
15-point lead on energy.

What I'm curious about is, when did the conventional wisdom change? Of course, the fact that Bush presided over the enormous economic crisis probably had a big impact, but the swing is so dramatic that the Republicans must have been eroding credibility on that front for quite a while. When did the Republicans last have an edge on the Democrats in the eyes of the electorate when it comes to the economy?