The symbolism is not lost on the White House: US President Joe Biden heads Thursday to Philadelphia, the cradle of American statehood, to deliver a rare primetime speech on what he calls "the battle for the soul of the nation."

His speech, set for 8:00 pm local time (0000 GMT), will take place near the building where the Declaration of Independence and the US Constitution were adopted more than two centuries ago.

Pennsylvania, the eastern US state that includes Philadelphia, may also prove key to the crucial midterms elections in November. The Democratic president will visit the state three times this week alone.

White House spokesman Karine Jean-Pierre has already signaled that the 79-year-old leader will mince no words in his speech attacking his opponents.

"The president thinks that there is an extremist threat to our democracy," she told reporters Wednesday.

And the threat has a name: "MAGA" or "ultra-MAGA" Republicans who embrace former president Donald Trump's "Make America Great Again" ideology.

"They just don't respect the rule of law," said Jean-Pierre before she called out several Republican officials and lawmakers by name for urging violence against public figures, a move that is highly unusual for a White House press briefing.

"The president believes, which is a reason to have this in primetime, that there are... a majority of Americans who believe that we need to... save the core values of our country," said Jean-Pierre.

The theme of Biden's speech Thursday harks back to an article he published in the influential American magazine The Atlantic in 2017, after a deadly white nationalist rally in the city of Charlottesville. The march in the southern state of Virginia made him decide to run for president.

"We are living through a battle for the soul of this nation," Biden wrote then.

After his election in 2020, the veteran politician initially planned to wage this battle through dialogue with moderate Republican lawmakers, and through economic and social policies aimed at the middle class.

But the rhetoric of reconciliation has died down, as Biden faced a Republican party still influenced by Trump.

Instead, opinion polls seem to show that Biden would benefit from being more aggressive towards his opponents. Last week, Biden accused Trump's supporters of being consumed by "semi-fascism."

The latest opinion poll from Quinnipiac University, released Wednesday, shows him with a 40 percent approval rating, still very low, but a significant improvement over the 31 percent recorded in July.

Moreover, according to the same survey, 67 percent of Americans now believe that their democracy is in danger, compared to 58 percent in January.

The Democrats are hoping for an upset in the November elections, in which all of the seats in the House of Representatives and a third of the Senate seats are on the ballot. Traditionally, the midterms don't favor the ruling party.

Things have been going well for Biden lately, however, with inflation slowing, a series of his landmark reforms finally pushed through Congress, Trump fighting off a series of criminal investigations, and -- most importantly -- the Republicans' anti-abortion efforts appearing to be turning against them.

This would be enough to give hope to the Democrats, who are battling to keep their hold on the House and preserve their Senate majority or even strengthen it.

And Pennsylvania will be crucial for any of that to happen.

Biden already traveled to the battleground state on Tuesday, and he will return there on Monday to celebrate Labor Day with Democratic Senate hopeful John Fetterman.

Trump is also planning an appearance in Pennsylvania on Saturday to support his candidate in this race, Mehmet Oz.