Donald Trump, faced with opposition inside and outside his party, plans to renew the nationalist themes that built his base and amplify his no-holds-barred attacks against Hillary Clinton to try to depress Democratic voter turnout, his advisers said.

Following the release of a tape-recording of his lewd comments about women and several high-profile Republican defections over the weekend, Mr. Trump has effectively given up the conventional wisdom of trying to reach voters far outside his core of support, one high-level Republican supporter said….

Mr. Trump, in fact, is trying to use his break with many party leaders as a lever to ramp up support among his base, which includes many voters who feel equally estranged from the party establishment.

The decision means that a campaign already marked by intensely personal attacks is primed to grow even uglier in the remaining four weeks. Mr. Trump plans to keep up a relentless assault on Mrs. Clinton, including her use of a private email server and allegations about her husband, former President Bill Clinton, with the intention of keeping some of her supporters home on Election Day, his advisers said.