What was certainly right about Trump’s tweet was its timing. The S&P 500 closed marginally lower on Thursday, ending an 9-day rally that ran since 7 February. As this includes a weekend, the rally amounted to a 7-day winning streak.
It’s true that winning streaks of such length rarely occur, but they are not quite as exceptional as Trump wants you to believe.
Stock market hits new high with longest winning streak in decades. Great level of confidence and optimism - even before tax plan rollout!— Donald J. Trump (@realDonaldTrump) February 16, 2017
We need to go back more than three years to find a S&P 500 winning streak exceeding February 2017’s 7 days: to the period between 2 and 11 September 2013, to be precise. But still: a few years is not ‘decades’.
Conclusion: not true
Our conclusion must be that the stock market was on its longest winning streak in several years when Trump sent his tweet, not the longest winning streak in decades. We have therefore caught Donald Trump tweeting an alternative fact here.