Inside the Battle for America’s Most Consequential Battleground State

When Vice President Kamala Harris rolled out her economic agenda, she went to Pittsburgh. When she unveiled her running mate, she went to Philadelphia. And when she had to pick a place for Barack Obama’s first fall rally this Thursday, it was back to Pittsburgh.

Former President Donald J. Trump has earmarked the greatest share of his advertising budget for Pennsylvania and has held more rallies in the state than in any other battleground since Ms. Harris joined the race — including two on Wednesday and three in the last week.

Welcome to the United States of Pennsylvania.

There may be seven main battlegrounds in the race for the White House in 2024, all of which could prove crucial. But Pennsylvania stands apart as the state that top strategists for both Ms. Harris and Mr. Trump have circled as the likeliest to tip the election.

Both candidates are pouring more money, time and energy into the state than anywhere else, with Ms. Harris, Mr. Trump and their allies set to spend $350 million just on television ads in Pennsylvania — $142 million more than the next closest state and more than Michigan and Wisconsin combined.

Part of Pennsylvania’s pivotal role is its sheer size: The state’s 19 electoral votes are the biggest prize of any battleground. Part of it is polling: The state has been virtually tied for months. And part of it is math: It is daunting for either Mr. Trump or, especially, Ms. Harris to reach the 270 Electoral College votes needed to win without it.