The biggest names in Democratic and Republican politics – Joe Biden, Barack Obama and Donald Trump – are firing up crowds in the same battleground state ahead of the US’s midterm elections.

The former presidents and Mr Biden descended on Pennsylvania, where all hope to tip the balance in the November 8 elections as momentum shifted to the Republicans.

It came as Mr Trump gave the surest sign yet he could soon confirm his intention to run for president in 2024. An announcement is expected on within days.

At a rally in Sioux City, Iowa, Mr Trump told his supporters to “get ready” and that “we are going to take back our magnificent White House”.

“In order to make our country successful and safe and glorious, I will very, very, very probably do it again, OK? Very, very, very probably,” he said.

“Get ready. That’s all I’m telling you. Very soon. Get ready. Get ready.”

Mr Trump is tipped to announce his run after the wedding of his youngest daughter Tiffany on November 12 at his Mar-a-Lago home.

Flags fly in support of Donald Trump ahead of a rally in Pennsylvania. Photo: Getty

Meanwhile former president Obama capped a five-state tour aimed at stemming his party’s losses in Tuesday’s congressional elections with appearances alongside Democratic Senate nominee John Fetterman and Mr Biden.

Former president Trump was to round up support for his hand-picked Republican Senate nominee, celebrity doctor Mehmet Oz — better known as Dr Oz — and Republican gubernatorial nominee Doug Mastriano at a rally in Latrobe, south-east of Pittsburgh.

As he has in a steady stream of rallies since leaving office, Mr Trump was also working to maintain his own profile as he contemplated launching a third run for the White House after the midterms, according to advisers.

That could set the stage for a Biden-Trump rematch. However, some Democrats say heavy losses for Mr Biden’s party on Tuesday could increase pressure on the President to step aside and let someone else carry the party’s mantle in 2024.

The Fetterman-Oz Senate race is one of three critical contests, along with Georgia and Nevada, that will determine whether Democrats hold onto their razor-thin majority in the Senate, and with it the power to confirm Mr Biden’s nominees to posts ranging from his cabinet to the Supreme Court.

Repulican candidate Dr Mehmet Oz, who shot to fame on the Oprah Winfrey Show as Dr Oz. Photo: Getty

Non-partisan election forecasters and polls show Republicans are heavy favourites to win control of the House of Representatives, with the Senate a toss-up.

Control of even one of those chambers would give Republicans the power to block Mr Biden’s legislative agenda and launch potentially damaging investigations.

Both parties have lavished attention on Pennsylvania both because of the strategic importance of the race and because of its voters’ history of swinging from one party to the other in the past four presidential elections.

Biden unpopular

Mr Fetterman, the state’s lieutenant governor, held a commanding lead in the race throughout the summer, which Dr Oz has whittled away in the past two months.

Some factors may be local: A stroke this spring forced Mr Fetterman to scale back his campaign schedule and has affected his speech.

But Dr Oz’s gains also reflect a nationwide momentum shift in favour of Republicans, as voters’ focus on inflation and crime has proven more durable than concerns about abortion.

Democrats’ early lead in several other Senate races, including in Georgia and Nevada, have also shrunk or evaporated in recent weeks.

Also playing against Democrats is Mr Biden’s unpopularity. Only 40 per cent of Americans approve of the President’s job performance, according to a Reuters/Ipsos opinion poll completed on Tuesday.

Barack Obama lends his star power to the campaign in Pennsylvania. Photo: Getty

Mr Obama has, by contrast, been tearing up the campaign trail in recent days in the nation’s most fraught battlegrounds – including Georgia, Michigan, Wisconsin and Nevada.

One bright spot for Democrats is Pennsylvania’s gubernatorial race. Democratic lawyer General Josh Shapiro holds a commanding lead against Doug Mastriano, a Republican state senator whose far-right stances have failed to connect with voters.