Expecting the S&P 500 Index to build on Monday’s 0.8% advance through the rest of this quarter may be wishful thinking, based on history. The index had its worst performance in the third quarter between 1980 and 2018. Gains in the third quarter averaged 0.3%, far below the comparable figures of 2.6% for the first quarter, 2.7% for the second and 4.1% for the fourth. This year, the S&P 500 beat both the first- and the second-quarter averages.