Sun shines on the US Supreme Court building in Washington, DC Monday ahead of President Donald Trump's announcement of his nominee for a newly vacant seat on the court

Washington (AFP) - President Donald Trump was poised Monday to nominate a new conservative judge to the Supreme Court, a decision with momentous implications for America on everything from abortion to guns to immigration.

Trump kept the suspense running through the weekend, teasing the announcement for maximum dramatic effect, but by Monday afternoon was reported to have made his pick among a shortlist of four judges, all with solid right-wing credentials.

The decision – awaited eagerly by his conservative supporters, and with trepidation by his liberal opponents – was to be announced at 9:00 pm (0100 GMT Tuesday) in a prime time address from the White House.

At stake is nothing less than a paradigm shift on the court, with the retirement of Justice Anthony Kennedy handing Trump an opportunity to place a decidedly conservative stamp on the bench.

“I have long heard that the most important decision a U.S. President can make is the selection of a Supreme Court Justice,” Trump tweeted early Monday, after a weekend spent weighing his decision at his New Jersey golf club.

While Trump has already made one pick for the high court since taking office in January 2017, the vacancy left by Kennedy, announced late last month, has weightier implications.

For years Kennedy often served as the tie-breaking swing vote between conservatives and liberals on the nine-member bench.

The candidates on Trump’s shortlist are all steadfast conservatives. They are Brett Kavanaugh, a former adviser to George W. Bush; Raymond Kethledge, a strict interpreter of the US Constitution; Amy Coney Barrett, a devout Catholic and social conservative; and Thomas Hardiman, a staunch gun rights advocate.

All four federal judges have the endorsement of major Republican legal groups, most importantly the powerful Federalist Society. None is older than 53, meaning they could sit on the court for decades, allowing Trump to make a lasting imprint on the nation’s laws.

“From the perspective of judicial conservatives, Trump really can’t lose here,” Josh Blackman, an associate professor at South Texas College of Law, told AFP.

“He could throw a dart on that list” and conservatives would be happy.

- Rush to fill seat -

In recent years the Supreme Court has made landmark decisions on fundamental and often politically charged issues ranging from same-sex marriage, abortion, gun rights, corporate money in elections, and free speech.

US president Donald Trump will nominate a new justice for the Supreme Court who could turn the court deeply conservative for decades

In the coming year the court might have to consider Trump’s powers and rights in the investigation into links between his presidential campaign and Russia, and whether he sought to obstruct that probe.

Trump has moved quickly to make a nomination while Republicans hold a bare majority in the Senate, which needs to approve the appointment.

Republican congressional leader Mitch McConnell has reportedly tried to nudge Trump towards one of two candidates – Hardiman or Kethledge – seen as presenting fewer obstacles to a Senate confirmation.

Within Republican ranks, Senator Susan Collins has already signalled she could break with her party if Trump taps someone hostile to the landmark 1973 Roe v. Wade ruling that guaranteed women’s access to abortion.

If the nomination is delayed and Democrats capture an extra seat in the Senate in November elections, Trump could be forced to compromise with liberals in order to fill Kennedy’s seat.

- Conservative shortlist -

Trump promised Sunday to choose an “exceptional person” for the post, but some Democrats were already signalling blanket opposition.

“I will oppose the nomination the president will make tonight because it represents a corrupt bargain with the far right, big corporations, and Washington special interests,” Senator Bob Casey said.

By Monday Barrett, at 46 the youngest and the only woman of the four, was being widely discounted due to her relative inexperience and her strong views as a social and religious conservative.

US Supreme Court

Kavanaugh, 53, began his career as a clerk to Kennedy. As a judge on the US Court of Appeals in Washington he has written opinions on some of the nation’s most sensitive issues. He recently voiced disagreement with a court decision allowing an undocumented teenage immigrant to get an abortion.

He also has expressed a broad interpretation of what constitutes obstruction of justice, a position which could be risky if the Russia investigation leads to impeachable allegations against Trump.

Kethledge, 51, sits on the Sixth Circuit appeals court. He is seen as an “originalist” – a conservative school that seeks to interpret the US Constitution based on the thinking of the country’s founding leaders, and often takes narrow views in cases of individual rights.

Hardiman, 53, a judge on the federal court in Philadelphia, is less known in terms of his legal philosophy, but has working-class roots that could make him attractive to the American public.