Going by the pattern, we'll have two more 200 MA intersections then we're good to go in another multi decade bull market. I don't know when, but Barron's has said 2020 will be the start of the recession. Going by the chart, to get back to the 200 month MA we will need to at least go down to 1650 on the index. This is about a 50% retraction.
Another way to interpret it is we've had our three touches in 2009, '10 and '11. They are very close together though. In the 1930s recession, the first touch/support was in '21, the last in '42, a 21 year stretch before the next bull market. The one in '75 was much shorter, first support '74, second '78. A four year stretch. So perhaps governments have gotten more skilled at managing recessions and it's realistic to expect this one to be done and dusted in three years.
Tradingview has the data back to the 1870s. Just type SPX into the ticker box and look for the Standard & Poor 500 index. This is a log chart to make it easier to compare moves across time.