WASHINGTON, DC, United States (AFP) — Donald Trump vowed a new US “golden age” as he took the oath for a historic second presidential term Monday, but focused most of his dark inaugural speech on touting hardline policies to reverse what he called “American decline”.

In an often divisive address, the 47th president took aim at illegal immigration and the culture wars as he capped the most remarkable comeback in US political history.

“The golden age of America begins right now. From this day forward our country will flourish and be respected again all over the world,” Trump said in the US Capitol, where his inauguration was held indoors for the first time in decades due to freezing weather.

The Republican also referenced the assassin’s bullet that grazed him at a rally during his victorious election campaign, saying: “I was saved by God to make America great again.”

While promising renewal, Trump harshly denounced what he said had been a “betrayal” of Americans by a “radical and corrupt establishment” under outgoing President Joe Biden.

“America’s decline is over,” said Trump.

Biden — who had earlier hosted Trump and his wife Melania at the White House for tea — watched stony-faced as his political nemesis read the last rites over his single term in office.

Trump also set out his foreign policy stall, saying he wanted to be a “peacemaker and a unifier” — but then saying the United States was “taking back” the Panama Canal and warning he would make liberal use of trade wars.

He also vowed to “plant the Stars and Stripes” on the planet Mars.

The billionaire — at 78 now the oldest person ever to take the presidential oath — was set to kick-start his new term with a host of executive orders.

“I will declare a national emergency at our southern border” with Mexico, Trump said to loud cheers inside the ornate Rotunda hall, vowing to deport “millions and millions” of illegal immigrants.

Trump said his Government would recognise “only two genders, male and female”, ending the current practice of providing a third gender option in some settings.

He will also pull Washington out of the Paris climate accord aimed at halting global warming.

While Trump was a political outsider at his first inauguration in 2017 as the 45th president, this time around he was surrounded by America’s wealthy and powerful.

The world’s richest man Elon Musk, Meta boss Mark Zuckerberg, Amazon chief Jeff Bezos and Google CEO Sundar Pichai all had prime seats in the Capitol alongside Trump’s family and Cabinet members.

Musk will lead a cost-cutting drive in the new Administration.

Former presidents Barack Obama, George W Bush and Bill Clinton all attended the ceremony with their spouses — except for ex-first lady Michelle Obama who pointedly stayed away.

Clusters of supporters watched the ceremony — normally viewed by thousands of people on the National Mall — on their phones outside the Capitol.

“I feel on cloud 10,” said Gregg Donovan, a 65-year-old from Hollywood wearing a top hat with a photo of Trump tucked into the brim, moments after Trump was sworn in.

While Trump refused to attend Biden’s 2021 inauguration after falsely claiming electoral fraud and inspiring a violent assault by supporters on the Capitol, this time Biden was keen to restore the sense of tradition.

“Welcome home,” Biden had said to Trump when he arrived for tea at the White House.

But it was a bitter departure for Biden, who was forced to drop out of the 2024 election against Trump at the last minute due to concerns about his age.

In the waning minutes of his presidency Monday, Biden issued extraordinary pre-emptive pardons for his siblings and their spouses to shield them from “politically motivated investigations”.

He also pardoned former COVID-19 advisor Anthony Fauci, retired general Mark Milley, and members of a US House committee probing the violent January 6, 2021 US Capitol attack by Trump’s supporters.

Trump attacked this soon after he was inaugurated, claiming falsely that Biden had pardoned people “guilty of very bad crimes”.

Trump is just the second president in US history to return to power after being voted out, after Grover Cleveland in 1893.

Another notable factor is Trump’s criminal record, related to paying a porn star hush money during his first presidential run — and a string of far more serious criminal probes that were dropped once he won the election in November.

For the rest of the world, Trump’s return means expecting the unexpected.

Russian President Vladimir Putin congratulated Trump ahead of the inauguration and said Monday he was open to talks on the Ukraine conflict — which Trump did not mention during his speech.

Israeli Prime Minister Benjamin Netanyahu also congratulated Trump — whose team helped broker a Gaza ceasefire deal — saying the “best days of our alliance are yet to come”.