I think the bull run holds so long as the 4 Horsemen, AAPL-AMZN-GOOGL-MSFT keep moving upwards.
Due to the weighted nature of the NDX, these 4 stocks alone accounted for 56% of the NDX gain in 2017. From the APR 2, 2018 low to today, the 4 Horsemen accounted for 67% of the NDX gain...