President Joe Biden is visiting Pennsylvania for the third time in less than a week, and he is returning just two days after his predecessor, Donald Trump, held a rally there. This highlights the importance of the battleground state to both parties as Labor Day ushers in a nine-week countdown to the pivotal midterm elections.

Trump spoke Saturday night in Wilkes-Barre, near Scranton, where Biden was born. The president made his own Wilkes-Barre trip last week to discuss increasing funding for police, decry GOP criticism of the FBI after the raid on Trump’s Florida estate and to argue that new, bipartisan gun safety measures can help reduce violent crime.

Two days after that, Biden went to Independence Hall in Philadelphia for a prime-time address denouncing the “extremism” of Trump’s fiercest supporters. On Monday, he’s attending Labor Day festivities in Milwaukee, in another key swing state, Wisconsin, before traveling to Pittsburgh for that city’s parade.

The White House says Biden will celebrate “the dignity of American workers.” The unofficial start of fall, Labor Day also traditionally kicks off political crunch time, with campaigns scrambling to excite voters ahead of Election Day on Nov. 8. That’s when control of the House and Senate, as well some of the country’s top governorships, will be decided.

Trump has endorsed candidates in key races around the country and Biden is warning that some Republicans now believe so strongly in Trumpism that they are willing to undermine core American values to promote it. The president said Thursday that the midterms will be a battle “for the soul of the nation,” the same slogan he used to win the 2020 election, and that “blind loyalty to a single leader, and a willingness to engage in political violence, is fatal to democracy.”

Biden added in that speech that “MAGA Republicans are destroying American democracy,” referring to Trump’s “Make America Great Again” campaign cry and pointing to incidents like last year’s mob attack on the U.S. Capitol.

Trump said during his Saturday rally that Biden’s Philadelphia appearance featured “the most vicious, hateful and divisive speech ever delivered by an American president.”

“He’s an enemy of the state,” the former president said.

Monday will see Biden return to another theme that was a centerpiece of his 2020 campaign, that labor unions burnished the middle class, which in turn built and strengthened modern American society.

Endorsements from key unions helped Biden overcome disastrous early finishes in Iowa and New Hampshire to win the Democratic primary, and eventually the White House. He has since continued to praise labor unions — even though many voters without college degrees, many working class, remain among Trump’s strongest bloc of supporters.

Mary Kay Henry, president of the 2-million-member Service Employees International Union, called Biden championing unions heading into the midterms “critical” and said that the labor movement must “mobilize in battlegrounds across the country to ensure that working people turn out.”