President Donald Trump, from a toss-up congressional district in New York on Friday, began testing his midterm-year message that was ostensibly on the economy. But he veered off-topic right from the start, going off on tangents about voter identification, crime in cities, transgender women in sports and "Dumocrats," his new chosen moniker for the opposition party.

President Trump said Friday he will not be attending his son Donald Trump Jr.’s wedding this weekend, citing government business. “While I very much wanted to be with my son, Don Jr., and the newest member of the Trump Family, his soon to be wife, Bettina, circumstances pertaining to Government, and my love for the...