Polls opened Tuesday in crucial US midterm elections that could decide the political future of both President Joe Biden and his predecessor Donald Trump — who has all but announced he will seek the White House again in 2024.

Biden’s Democrats are facing a gargantuan struggle to hang on to Congress, after a race the president has cast as a “defining” moment for US democracy — while Trump’s Republicans campaigned hard on kitchen-table issues like inflation and crime.

Trump — who has been heavily hinting at a new run — grabbed the election eve spotlight to flag “a big announcement” on November 15, while Biden made a final appeal to Democrats to turn out en masse at the polls.

“The power’s in your hands,” Biden told a rally near the capital. “We know in our bones that our democracy is at risk and we know that this is your moment to defend it.”

With polls showing Republicans in line to seize the House of Representatives, the increasingly far-right party eyed snarling the rest of Biden’s first term in aggressive investigations and opposition to spending plans.

Returning to the White House Monday night, Biden told reporters he believed Democrats would win the Senate — though conceding “it’s going to be tough” to retain the House and that his life in Washington may become “more difficult.”

If both the House and Senate flip, Biden would be left as little more than a lame duck.

With Congress out of Democrats’ hands, he would see his legislative agenda collapse.

That would raise questions over everything from climate crisis policies, which the president will be laying out at the COP27 conference in Egypt this week, to Ukraine, where Republicans are reluctant to maintain the current rate of US financial and military support.

An influx of far-right Trump backers in Congress would also accelerate the shift that has been taking place inside the Republican Party since the former real-estate tycoon stunned the world by defeating Hillary Clinton for the presidency in 2016.

Despite facing criminal probes over taking top secret documents from the White House and trying to overturn the 2020 election, Trump has been using the midterms to cement his status as the de facto Republican leader and presumptive presidential nominee.

In a typically dark, rambling speech to fans in Dayton, Ohio, Trump said, “if you support the decline and fall of America, then you must, you absolutely must vote for the radical left, crazy people.”

“If you want to stop the destruction of our country, then tomorrow you must vote Republican in a giant red wave,” he said — before teasing his 2024 announcement

Second Biden run?

Across the country voters called on their fellow citizens to cast their ballot in the midterms, which historically have low turnout.

“I would emphasize vote, vote, vote,” 24-year-old student Luke Osuagwu told AFP in Atlanta, Georgia.

“If you’re not voting, you can’t really stand for society or anything like that,” agreed Alethia McClenton, a 45-year-old Georgia Aquarium employee. “It’s very important that everybody goes out to do their part.”

More than 40 million ballots were cast through early voting options, meaning the outcome had already begun to take shape before election day.

Polls started to open on the East Coast at 6:00 am (1100 GMT), and begin closing 12 hours later.

Up for grabs are all 435 House seats, a third of the 100 Senate seats, and a slew of state-level posts. Four states are also holding referendums on abortion — California, Vermont, Kentucky and Michigan.

Senate races in Pennsylvania, Nevada, Arizona, Georgia, Wisconsin, New Hampshire and Ohio have narrowed to projected photo finishes, and any one of them could swing the balance of power.

But final results may not be known until days — or in some cases even weeks — after election day, setting the stage for what promise to be acrimonious challenges.

Trump has already claimed baselessly that swing state Pennsylvania “rigged” the midterms — reprising his playbook from the 2020 election which he falsely asserted was stolen by Biden.

Citing growing support for voter conspiracy theories among Trump and his Republicans, as well as their push to curb abortion access, Biden has warned that democracy and basic rights are at stake on Tuesday.

Republicans have countered that a vote for Democrats means more soaring inflation and rising violent crime, seeking to make the midterms a referendum on the president.

The outcome will likely determine whether Biden, who turns 80 this month and is the oldest president ever, will seek a second term in 2024 — or step aside.