That brings us to the funny thing about opinion polls. In this case, the eight percent who admitted they didn't know the answer are probably correct.
As much as Presidents like to take credit for the good times and avoid responsibility for recessions (and blame them on their predecessors), the White House's effect on the economy is not as strong as many people think. Fiscal policy (taxes, government spending, regulations) is largely determined by Congress and monetary policy (banking regulations, interest rates) is set by the folks at the Federal Reserve.
Presidents can fundamentally alter the economy by pushing through long-term, bold initiatives (Eisenhower's highway system; Kennedy space race) but it's difficult, if not impossible, to credit one person with the final results of national projects that take decades to complete.
In the foreign policy arena, the President has quite a bit of leeway as the Commander-in-Chief to make friends with potential trading partners or enemies with countries that refuse to participate in the global economy on America's terms. However, all those big decisions still need to be approved by Congress.
Of course, the President's economic positions still deserve our scrutiny, especially since he holds both veto and "cheerleader" power. But ultimately, let's not forget that it's the private sector that really creates economic growth.