WASHINGTON (Reuters) - With a second Supreme Court pick less than 18 months into his presidency, Donald Trump is poised to cement conservative control of the court and fire up supporters eager for a rightward shift on divisive social issues.

U.S. President Donald Trump arrives to speak at a rally in support of Rep. Kevin Cramer's run for Senate in Fargo, North Dakota, U.S., June 27, 2018. REUTERS/Kevin Lamarque

Shortly after Justice Anthony Kennedy announced his retirement on Wednesday, White House officials said Trump had an opportunity to shape U.S. justice for decades to come.

“It will further his agenda of remaking the courts,” said one senior White House official. “This is a legacy.”

Speaking of the selection at a rally in North Dakota on Wednesday night, Trump said: “We have to pick a great one. We have to pick one that’s going to be there for 40 years, 45 years.”

Kennedy’s replacement could be pivotal in paring back abortion rights, potentially even challenging the Supreme Court’s landmark Roe v. Wade ruling in 1973 that gave women a constitutional right to obtain the procedure.

Undoing or at least putting more limits on that ruling has been a dream of conservative activists and contributed to conservative Christian support for Trump that helped him win the presidency in 2016.

Although Kennedy was a conservative nominated by Republican President Ronald Reagan, he was seen as the “swing vote” on the court because he joined with liberal justices on some major issues, including expanding gay rights and upholding abortion rights.

By picking a social conservative to replace Kennedy, Trump would have a reliable 5-4 majority on the Supreme Court, even on some of those hot-button social issues.

While Trump did not make rolling back abortion rights a central plank of his campaign, many of the conservative rank and file want Roe v. Wade overturned and Trump promised to put anti-abortion justices on the Supreme Court.

But picking an ultra-conservative as his nominee would carry risk because Trump would have to rely on some moderate Republicans to win approval in the U.S. Senate, where his fellow Republicans have a narrow majority.

White House officials said Trump was likely to quickly begin interviewing candidates from a list of 25 people that the conservative Federalist Society helped draw up, with an eye to getting the new justice confirmed by the Senate in the autumn.

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They believe the timing could help Trump boost conservative voters’ enthusiasm and turnout at congressional elections in November. Republicans are fighting to maintain control of both houses of Congress, with opinion polls showing Democrats have a strong chance of winning back the House of Representatives.

“Any time you’re in a midterm election year, you’re going to have a concern about whether your base will turn out,” said one official. “A high-profile Supreme Court battle will certainly remind all your voters what is at stake.”

RECENT WINS

The sharply divided high court has already handed Trump a series of other wins in politically charged cases in recent weeks.

On Tuesday, it upheld Trump’s travel ban on people entering the United States from several majority-Muslim countries.

Led by Chief Justice John Roberts, the court during its term that started in October and ended on Wednesday repeatedly ruled for Trump on 5-4 votes with its four liberals dissenting.

Despite previously siding with liberal justices in some key cases, Kennedy was a reliable conservative vote during the latest term.

Those victories, coupled with Kennedy’s retirement, could embolden the administration’s lawyers, who are facing legal challenges on multiple fronts, including over Trump’s move to separate families who enter the United States illegally and his plan to rescind protections for “Dreamers,” young adults brought to he country illegally as children.

An open seat on the Supreme Court was an important factor in rallying conservatives behind Trump’s presidential election campaign in 2016. He used every opportunity to tell voters only he stood in the way of the court taking a turn to the left should Democrat Hillary Clinton win.

Trump quickly delivered on that promise by selecting Neil Gorsuch, who has become one of the most conservative justices.

Trump has also filled a record-breaking number of seats on the influential federal appeals courts - appointing 21 judges in total – with the enthusiastic backing of the Senate, which votes to confirm them. Trump has also appointed 20 District Court judges.

Trump appeared to be excited on Wednesday about the new opportunity to reshape the federal judiciary in a conservative direction.

“We will begin our search for a new justice of the United States Supreme Court. That will begin immediately,” Trump said at the White House. “And hopefully we’re going to pick somebody who will be as outstanding.”