Gabriel Lopez grew up in a family of Democrats in the Kensington neighborhood of deep-blue Philadelphia. So in 2016, the first presidential election he was old enough to vote in, he picked Hillary Clinton over Donald Trump. But Lopez, now 27, says his views have changed. He switched his registration to Republican this year, and he plans to vote for Trump, who’s running for president a third time. “Democrats keep saying [Trump] is going to bring down the economy, but he was already...