Access to abortion and health care will be at the heart of the looming battle over the appointment of a new Supreme Court justice, with all eyes on a handful of senators with the power to endorse or block President Donald Trump's choice.

Democrats are hoping to prevent Trump from tilting the court to the hard right by tapping an ultra-conservative to replace Justice Anthony Kennedy, the tie-breaking vote between the liberals and conservatives on the nine-seat bench who retires at the end of July.

At stake, they argue, is the landmark 1973 Roe v. Wade ruling that enshrined women's legal right to abortion at the national level.

"President Trump's own words tell us that his nominee to the Court will almost certainly vote to overturn Roe v. Wade and eviscerate affordable access to health care for millions of Americans," senior Democrat Senator Chuck Schumer wrote in a New York Times op-ed Monday, laying down the party's strategy for the coming fight.

The moderate Kennedy, 81, for years kept the powerful court from moving decisively into a conservative bias favored by Republicans. His announced retirement has thrown that balance into question.

Trump said last week that Kennedy's successor -- who like all Supreme Court justices will be appointed for life -- would be nominated from among a list of 25 candidates endorsed by the stridently conservative Heritage Foundation and Federalist Society.

The president is set to announce his choice on July 9. He has reportedly interviewed four candidates so far.

White House spokeswoman Sarah Sanders said that although Trump opposes abortion, he is not pressing the candidates on their views of specific cases.

"He's looking for individuals that have the right intellect, the right temperament and uphold the Constitution," she said.