The vast majority of the economy is, quite simply, out of the control of politicians.
So we can have all the discussions about blaming President A for something and praising President B for something else...when they had little or nothing to do with it.
I love this quote simply because it's the antithesis of Republican philosophy for the last 20 years. Reagan was loved because he offered a tax cut that 'stimulated' the economy (according to Republicans). Hell, the loss of George Bush (I) was due to his tax hike which 'hurt the economy' (according to Republicans).
Personally, I felt this was hogwash. The President of the US can not control the economy (imo). But even Clinton's 8 years of fairly good economic status didn't detour this train of thought, rather Republicans, instead of crediting Clinton with anything, merely stated that Clinton was riding on Reagan's changes (now 20 years into the future).
Ah, but put a Republican president in charge and add a downturn to the economy (which appeared right on schedule) and suddenly the tune changes. Suddenly Presidents can't truly affect the economy and it's fairly foolish to expect them to be able to do so.
Gotta love it.