Why do Americans trust Republicans on the economy when they do so poorly every time?  Let's look at the GDP growth rate:

Here it is graphically (data for Obama's second term not yet available when published in 2016):


And by party control of Congress:

The myth that successful businessmen are good managing the U.S. economy is a myth, one promulgated by the Republican Party, Fox News, and most media outlets.  Hoover (remember him) brought us the Depression, G.W. Bush lost money on each of his business ventures, and Trump has destroyed company after company, and now the U.S. economy.  Fifty-seven percent of Americans believe that Republicans do better with the economy, and of course you heard it at this years Republican Convention along with all the other lies.

These data are from:  Blinder, Alan S., and Watson, Mark W. (2016). Presidents and the US economy: an economic exploration.  American Economics Review 106: 1015-1045.

They are both from the Department of Economics and the Wilson School of Public and International Affairs, Princeton University.