As detailed in the chart below, June is the second worst performing month of the year for the Dow Jones Industrial Average. This is second only to September; historically, the worst performing month of the year . This year, May's performance was slightly more than 4.6% and far above the historical average return for the month.
Additionally, the equity markets tend to be strongest in pre election year periods. However, this outperformance tends to occur in the first 6-7 months of that year.
Source: Chart of the Day