Donald J. Trump leads President Biden in five crucial battleground states, a new set of polls shows, as a yearning for change and discontent over the economy and the war in Gaza among young, Black and Hispanic voters threaten to unravel the president’s Democratic coalition. The surveys by The New York Times, Siena College and The Philadelphia Inquirer found that Mr. Trump was ahead among registered voters in a head-to-head matchup against Mr. Biden in five of six key states: Michigan,...