THE shock retirement of a US Supreme Court justice has opened the door for Donald Trump to establish a conservative majority in the nation’s highest court.

A momentous confirmation battle was sparked on Wednesday after justice Anthony Kennedy – a singular voice on the court whose votes have decided issues on abortion, affirmative action, gay rights, guns, campaign finance and voting rights – stunned Washington by announcing his retirement plans.

Trump announced he would start the effort to replace Kennedy “immediately” and would pick from a list of 25 names that he updated last year.

“We have to pick a great one. We have to pick one that’s going to be there for 40 years, 45 years,” Trump told supporters at a rally in Fargo, North Dakota, on Wednesday evening.

Senate majority leader Mitch McConnell declared that the Senate will decide on Kennedy’s successor in the autumn.

The justice’s departure gives the Republicans a chance to tip the balance of the court.

It already has four justices picked by Democratic presidents and four picked by Republicans, so Trump’s pick could shift the ideological balance toward conservatives for years to come.

Republicans also have a chance to make judicial nominees a top campaign issue, which could help motivate conservatives and evangelicals to vote in November’s mid-term elections.

The strategy worked in 2016, when Republicans rallied around McConnell’s successful block of Barack Obama’s nominee to the court, Merrick Garland.

If Republicans unite behind Trump’s selection, there is little that Democrats can do to stop it.

The Supreme Court fight is could also trigger a flood of new campaign cash.

“It’s a game changer,” said Republican strategist Chris Wilson. “There’s no piece of legislation, no executive order, no Supreme Court decision that would have created the level of motivation that an empty seat does.”

Republican Senator Ben Sasse of Nebraska, a member of the Judiciary Committee, bluntly talked of the “blood sport” likely to be triggered by the nomination fight.

“Americans ought to aim higher,” he said.

Republicans changed Senate rules last year so that Supreme Court nominees cannot be filibustered, meaning only 51 votes will be required to confirm.

Last year, Trump’s first nominee to the court, Neil Gorsuch, was confirmed 54-45, with votes from three Democrats senators.

While Republicans aim for quick action, Democrats argue that any decision should be put on hold until after mid-term elections, citing McConnell’s 2016 moves.

Senate minority leader Chuck Schumer claimed it would be the “height of hypocrisy” to vote sooner. He said the voices of millions of American voters “deserve to be heard”.

McConnell refused to consider Garland because it was a presidential election year. He said the seat should be left open for the next president to fill.

Senator Chuck Grassley, the chairman of the Judiciary Committee, explained that the 2016 delay on Supreme Court confirmations only applied to presidential election years.

He noted that Justice Elena Kagan was confirmed in 2010, a mid-term election year.

Another flashpoint in the court debate will be abortion rights. Kennedy sided with four liberal justices to legalise abortions nationwide in 1992 but that ruling is now under threat from hard line Republicans.

Schumer said the Senate should reject “on a bipartisan basis any justice who would overturn Roe v Wade or undermine key health care protections”.