Donald Trump, the Republican presidential candidate is set to hold a rally in Pennsylvania today, his fourth campaign stop in the state this month. Erie, located in the northwest corner of Pennsylvania, will host the former president at 2 pm local time.

This rally comes one month after his running mate, US Senator JD Vance held a similar event in the same city. Trump has another rally scheduled in western Pennsylvania for October 5.

Pennsylvania has emerged as a crucial battleground state in the 2024 election, with many of Trump’s allies considering it the most important state to win. The state’s significance stems from its large population and the substantial number of electoral votes it awards, making it a critical factor in determining the overall winner of the election.

In fact, among the seven competitive states that both Trump and Vice President Kamala Harris have a realistic chance of winning, Pennsylvania stands out as the most populous and electorally valuable.

Trump allies broadly believe that if the former president beats Harris there, he is likely to return to the White House. But if Trump loses to Harris in Pennsylvania, the vice president has the inside track, in their opinion.

In a reflection of the stakes, Harris and Trump have spent hundreds of millions of dollars on ads in Pennsylvania in the months before the election, more than any other state in both gross and per capita terms.

Erie, the site of Trump’s rally, is a battleground inside a battleground. Erie County is one of two Pennsylvania counties that favored Trump in the 2016 election against Democratic candidate Hillary Clinton before favoring President Joe Biden against Trump in 2020.

Trump narrowly won the state and the election overall in 2016, before losing both in 2020.

This time around, Pennsylvania is again competitive, according to surveys. Harris leads Trump by 1.6 percentage points in the state, according to an average of polls maintained by polling and analysis website FiveThirtyEight. That difference is well within almost all polls’ margin of error.

Trump’s next rally in Pennsylvania, on Oct. 5, will take place in Butler, about 100 miles (160 km) south of Erie. That town was the site of a failed assassination attempt on Trump in July. A bullet grazed the former president’s ear.

With inputs from agencies.