I couldn't help but do the numbers:
S&P 500 closing prices
3386   2/19/20 all time high
2507   12/31/18 at close of 2018

It would take a 26.0% drop from the all time high to erase the gains of 2019
so that would be a serious plunge but not a great crash. (We're already 12.8% down from the all time high as of Friday's close)
(They usually measure the severity of a drop from the previous all time high, particularly one that's close in time like this one).

That's an ordinary bear market

https://www.thebalance.com/u-s-stock-bear-markets-and-their-subsequent-recoveries-2388520


So yes, it's going to happen in the not-so-distant future. The reason we've gone this long without one is because of how far down we went in the last one (57% drop from peak to trough as measured by the S&P 500).

So if it's going to happen in the next one, two, three, four years, I'd much much rather have it happen before November than after.

I am convinced Trump would probably win if the economy was where it was in January and early February with substantially sub-4% unemployment and monthly job gains in the 150,000-200,000 range.

Since WWII, when the economy was good under a Republican president, a Democratic presidential candidate has never won. Democrats trying to unseat the Republicans only do so when the economy is trending poorly (or crashing). Some analysis I read in the Washington Spectator, but I think its true, although the number of sample points obviously is quite small.

I'm pretty sure Trump would lose if we had a recession begin, along with a bear market (or worse) but the NBER, which is the official score-keeper of recessions, takes a year to call one after it starts. So that's too late. But the unofficial but widely used definition of recession in the meantime is two back-to-back quarters of negative real GDP growth. Before the election that means Q2 and Q3 both have to be negative. Q3 ends September 30, and the first estimate of Q3 GDP will be in late October.

But anyway if things are obviously crashing (and with job losses), people won't need to wait to see the Q3 estimate to have their votes influenced.

Counting the so called double-dip recession of 1980-82 as one recession,

we've had 8 recessions since 1945: 1953, 1958, 1960-61, 1973-75, 1980-82, 1990-91, 2001, 2007-2009
https://en.wikipedia.org/wiki/List_of_recessions_in_the_United_States

which averages one every 9.4 years on average (starting from and including 1960-61, its one every 10 years on average).

either way we're overdue since the last one ended in June 2009.

And not to mention if the coronavirus turns out to be bad...