Five days before Election Day, the battle for Arizona has grown so fierce that Blake Rebling keeps losing his “Republicans for Harris” yard signs.

One was thrown into an alley, Mr. Rebling, 38, said. Others were nabbed at night. Last weekend, his children drew their own replacements, adding in green marker, “Don’t steal this sign!”

Four years ago, the family’s upper-middle-class neighborhood was part of a leftward shift across metro Phoenix that helped President Biden capture Arizona by 10,457 votes. It was Mr. Biden’s slimmest margin of victory in any swing state, and the first time a Democrat had won Arizona since 1996. Now, their leafy street is part of a fast-changing state torn in two — divided over abortion rights, immigration and festering distrust in elections.

Hanging over everything: Will a state that has been drifting Democratic in recent years reverse course and give former President Donald J. Trump a second chance?

Down the street from Mr. Rebling, Tim Harding and his family hoisted a Trump flag and planted yard signs saying, “Take America Back!” Mr. Harding, 45, said his house-painting business is suffering because of higher costs and a slowdown in home sales. He is one of thousands of new voters who moved to Arizona from California, and said he was eager for his first vote here to be against the liberal politics he had fled.

“Another four years of that?” Mr. Harding asked. “It’s really scary.”

As both parties brave the unseasonable late October heat to ring doorbells and barnstorm far-flung corners of the state, on the hunt for remaining undecided voters, they each have compelling cases for victory in a state whose politics are being transformed unpredictably by new residents like Mr. Harding and the rapid growth of U.S.-born Latino voters.

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