Richard Wolf

USA TODAY

WASHINGTON — Among the myriad concerns on the minds of hundreds of thousands of women demonstrating in the nation's capital Saturday, their constitutional right to an abortion may be paramount.

And, for the time being anyway, protected.

Despite President Trump's opposition to abortion and his vow to nominate Supreme Court justices who share his view, the court isn't likely to reverse its 43-year-old decision in Roe v. Wade anytime soon.

The president, in fact, has admitted as much, acknowledging before the election that overturning the 7-2 ruling "has a long, long way to go." His nomination in the coming days of a replacement for the late Justice Antonin Scalia would restore a fourth vote on his side of the ledger. Trump likely still would need another appointment, and possibly two, to convince Chief Justice John Roberts and other conservatives that the time for overruling its 1973 precedent had come.

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There are several reasons: The high court does not like to overrule its own precedents, particularly those that have stood for decades and affected millions of people. When it does, it tends to do so incrementally, which could mean allowing states to impose more restrictions on abortion without eliminating the federal right entirely.

Then there is the issue of who sits on the court and how strongly they feel about abortion. Though Justice Clarence Thomas and whoever Trump selects might be ready to jettison Roe, neither Roberts nor Justice Samuel Alito is committed to doing so. Roberts, in particular, is an incrementalist who has the court's reputation as an institution to consider.

"Roberts does not have a personal passion to overturn Roe," says Neal Devins, a law professor at William & Mary Law School who has written on the subject. "It would require a lot for it to happen."

The women marching for reproductive rights and other causes Saturday would get inspiration from a show playing just a few miles away in Washington. "Roe," by playwright Lisa Loomer, depicts the lives of Norma McCorvey -- who became "Jane Roe" in the case -- and her attorney Sarah Weddington, from McCorvey's initial quest for an abortion through the high court case and her later metamorphosis into an abortion rights opponent.

While offering perspectives from both sides through an array of characters, the play includes an aside from Justice Harry Blackmun, who wrote the opinion legalizing abortion: His wife and daughter, his character says, played important roles in convincing him which side to take.

That decision balanced a woman's right to have an abortion against the desire of some states to protect the unborn by allowing increased levels of regulation during the last trimester of pregnancy. Two decades later in Planned Parenthood v. Casey, the court upheld that basic right but allowed more limits based on the viability of the fetus.

Justice Samuel Alito's replacement of Justice Sandra Day O'Connor led the court in 2007 to uphold a federal law banning late-term, or "partial birth," abortions. After Scalia's death last year, the court voted 5-3 against a Texas law that imposed harsh requirements on abortion clinics and doctors who perform abortions.

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Those five justices — Anthony Kennedy, Ruth Bader Ginsburg, Stephen Breyer, Sonia Sotomayor and Elena Kagan — remain on the court. To reverse Roe would require one or more of them to leave while Trump or another opponent of abortion rights is president.

If, on the other hand, the court remains closely divided but with five justices opposed to abortion, most analysts predict it will move slowly — perhaps by upholding state restrictions greater than those allowed under Casey.

With most state legislatures beginning 2017 sessions this month, abortion rights groups are watching for such restrictions. Nancy Northup, president of the Center for Reproductive Rights, says more than 20 states are likely to ban abortion almost immediately, and another 20 or so — including California, Florida and New York — are likely to preserve abortion rights. The others would be battlegrounds.

Trump has said the issue would "go back to the states" if the Supreme Court were to overturn Roe -- a prospect that's about the best anti-abortion groups can hope for. "That's what a federalist system means," says Clarke Forsythe, acting president and senior counsel at Americans United for Life.