I use to move 100% to the bond fund whenever a republican was president
It looks like you avoided a bloodbath under Bush II. Reagan and Bush I had decent returns. I don't have total return data going back before 1976. By total return, I mean including reinvested dividends.
(Democrats have better records from some tabulation I saw in Forbes a few years ago, and going back to Truman).
The below are the total returns of VFINX, Vanguard's S&P 500 index fund. The Adjusted Close column includes reinvested dividends and other distributions, so is the basis of the below.
https://finance.yahoo.com/quote/VFINX/history
Measuring from the last close before Inauguration Day.
Total Average Annualized Returns of VFINX under Republican presidents
7.44% Benedict Dotard (1/19/17 close to 12/31/18 close)
-3.93% Bush I
14.47% Bush II
10.70% Reagan
.... Eisenhower, Nixon, Ford -- VFINX doesn't go back this far
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Some people measure Benedict Dotard's returns from the election. Measuring from election afternoon close (11/8/16) thru 12/31/18 close, the average annualized return has been 9.78%
As for 2018, the year we just suffered through, the annualized total return is MINUS 4.43%.
Measured from the Sept 20 peak, the S&P 500 itself is down 14.5% (I didn't include reinvested dividends in this particular number, because that wouldn't change that number much over a 3 month period, maybe 0.5 percentage points at most)
As the bull market that began in 2009 continues to age, and Dottie gets more erratic, and as the new Congress harasses him ...
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I'm not hawking VFINX, BTW, I use it because it is the oldest S&P 500 index fund, so the data goes back further than anyone else's (back to 8/31/76). There are other low expense ratio S&P 500 index funds out there, that might track the S&P 500 just as well or better. And S&P 500 ETFs too.
I use S&P 500 index funds because their returns include reinvested dividends (very important) and include (are net of) expenses (very important too). This is as close as one can get to investing in an index.
I have not found anything that will allow me to find the return of the S&P 500 itself, with reinvested dividends, from any date to any date of my choosing. And VFINX only goes back to 8/31/76. That's one reason why I haven't tried to figure out Eisenhower, Nixon, and Ford's record.