U.S. President Joe Biden took aim at hardcore supporters of former President Donald Trump Thursday and accused them of taking America "backwards" by undermining basic freedoms.

The speech comes at a time when Biden seeks to seize political momentum in a national address ahead of key midterm elections.

In excerpts of the primetime speech Biden delivered in Philadelphia, the cradle of U.S. democracy, the president called out the "MAGA" Republicans who embrace Trump's "Make America Great Again" ideology.

"MAGA forces are determined to take this country backwards," the 79-year-old leader charged. "Backwards to an America where there is no right to choose, no right to privacy, no right to contraception, no right to marry who you love."

Biden's speech – set for 8 p.m. (12 a.m. GMT) – took place near the building where the Declaration of Independence and the U.S. Constitution were adopted more than two centuries ago.

With control of Congress for the remainder of his first term in the balance in November's elections, Biden did not mince his words in what was billed as an address on the "battle for the Soul of the Nation."

"Tonight I have come here to the place where it all began to speak plainly to the nation about the threats we face," Biden said, according to speech excerpts.

"For a long time, we've reassured ourselves that American democracy is guaranteed. But it is not. We have to defend it. Protect it. Stand up for it. Each and every one of us."

But the president also sought to strike an optimistic note, speaking of the "power we have in our own hands to meet those threats" and the "incredible future that lies in front of us if only we choose it."

'Semi-fascism'

The theme of Biden's speech harked back to an article he published in The Atlantic magazine in 2017, after a deadly white nationalist rally in Charlottesville, Virginia that he says spurred his presidential run.

"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 talk of reconciliation has died down, as Biden faces a Republican Party still heavily influenced by Trump and polls seem to indicate the Democratic leader is better served by being more aggressive.

Last week, Biden accused Trump's supporters of being consumed by "semi-fascism."

The term sparked indignation in conservative ranks – with the Republican Senate Minority Leader Kevin McCarthy charging that it "vilifies" "tens of millions of hardworking, law-abiding citizens.

A new poll published Thursday by The Wall Street Journal shows that if the midterm elections were held today, 47% of eligible voters would cast ballots for Democrats, and 44% would vote Republican.

In March, the Republicans had a five-point advantage.

The Democrats are hoping for an upset in November, 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 and Trump fighting off a series of criminal investigations. Polls show widespread support for abortion rights, which could put many Republicans on the back foot.

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.

Historically a key battleground state in U.S. politics, the Keystone State will likely prove vital to both parties in the midterms – and Biden will visit three times this week alone.

Trump is also planning an appearance in the state on Saturday to support his candidate in the Senate race, U.S. Turkish television personality Mehmet Öz, better known as Dr. Oz.

'Free elections in danger'

Biden spoke in Philadelphia from behind bullet-proof glass and within earshot of chanting Trump-supporting protesters. He made his remarks at a venue meant to signal the historical significance of his appeal, near Independence Hall, where the U.S. Declaration of Independence and Constitution were adopted.

Some historians and legal scholars have cast the stakes in starker terms than Biden's political future, saying free elections and commitment to the rule of law hang in the balance.

They say losing Congress would not only make Biden a lame-duck president but also turn over control of certifying the results of the next presidential election to Trump sympathizers, some of whom never accepted Biden's 2020 victory and who have pledged to overhaul voting systems.

Biden alluded to the concerns, saying, "I will not stand by and watch elections in this country be stolen by people who simply refuse to accept that they lost."

The speech echoed Biden's signature 2020 campaign pledge to restore the "soul of the nation" and, by implication, purge the values associated with Trump. In the nearly two years since Biden was elected, Republican voters have mostly backed candidates aligned with the former president; more than half say they believe Trump rightfully won the election.

Confronted by threats after Trump's loss, one in five election workers polled this year said they may quit before the next presidential election.