(John Locher/AP)
Opinion writer

During one of his debates with John Kerry in 2004, President George W. Bush was asked what kind of justices he’d appoint to the Supreme Court in a second term, and gave what at first sounded to some like an odd reply. He wouldn’t appoint a justice, Bush said, who would issue a ruling like “the Dred Scott case, which is where judges, years ago, said that the Constitution allowed slavery because of personal property rights.”

What a universally condemned decision from 1857 had to do with anything was unclear, until it was pointed out that in the antiabortion movement, Roe v. Wade is often compared to Dred Scott. The reference was a dog-whistle, a way of telling voters opposed to abortion that Bush would appoint justices who would vote to overturn Roe without making it obvious to those who didn’t understand the code.

That story is relevant now because of how much the politics of abortion have changed. There are no more dog-whistles, no more messages intended for one audience that the rest of the electorate isn’t meant to hear, no more ambiguity. Abortion is front and center, and will be one of the key issues in the 2020 election.

A new poll from CNN shows how public opinion is beginning to shift:

Three-in-10 Americans say they would only vote for a candidate for major office who shares their views on abortion, according to a new CNN poll conducted by SSRS. That's higher than at any point in CNN polling on the topic from 1996 on.

Gender is a big factor in whether a person views abortion as a critical issue, even more than partisanship. Women (33%) — especially independent women (42%) and non-white women (39%) — are more apt to consider it a critical issue than men (26%). The share who say it is critical for them is about the same across party lines (33% for independents, 29% for Democrats, 28% for Republicans).

This isn’t some kind of sweeping transformation in public opinion, but any movement is notable. It’s being driven by events, particularly the aggressive moves in Republican states to pass laws outlawing abortion and force the Supreme Court to take up a case that could result in Roe being overturned.

To put it simply, Republicans are being more forthright about what they want, and Democrats are finally waking up to how threatened abortion rights really are.

For his part, as a candidate Donald Trump had none of George W. Bush’s subtlety; he just came out and said that he’d only appoint justices who would overturn Roe. “That will happen,” he said during one 2016 debate. “And that’ll happen automatically, in my opinion, because I am putting pro-life justices on the court.”

Yet somehow, pro-choice voters didn’t see the 2016 election as an emergency in the same way pro-life voters did. But now they’re starting to.

You can see it in what happened on Wednesday. A story from NBC News reported that Joe Biden maintains his support of the Hyde Amendment, which since 1976 has barred Medicaid from funding abortions in almost all cases, making them more difficult for poor women to obtain. Immediately, the other candidates began loudly proclaiming their opposition to the amendment. They didn’t mention Biden by name, but they have to. He’s not just the front-runner; this is also a rare case where his position is at odds with that of every one of the other 23 Democrats running for president.

While Biden wrote in the campaign book he released prior to his 2008 presidential run that he had had a “middle-of-the-road position on abortion for more than 30 years,” that’s no longer something a Democratic candidate would say with pride. The question for Democratic voters is whether their choice as nominee will be as committed to preserving abortion rights as Republicans are to destroying them.

The process of the campaign is likely to make those voters more committed and categorical about what they demand from their nominee on abortion. Their candidates will be competing to see who can present themselves as the most steadfast supporter of abortion rights, while at the same time, Republican-run states will probably keep passing restrictive laws that shine a light on the issue.

On the other side, the politics are more complicated. Most Americans oppose the GOP’s goal of overturning Roe, and many Republican officials were taken aback at the extremism of the outright ban that was passed in Alabama. While Democrats will be saying simply that they want to preserve abortion rights, Republicans will find themselves trying to argue that they want some restrictions but not others, and that they don’t quite agree with what some of their own brethren are doing.

It won’t be an easy case to make. Perhaps most importantly, those restrictive laws in Alabama, Georgia and elsewhere have been challenged in the courts, and could wind up before the Supreme Court some time in 2020. Just imagine what that will be like, if the fate of Roe v. Wade is decided just months before Election Day. There won’t be much room for middle ground.

Read more:

Karen Tumulty: On abortion, Biden shows he is out of step with his party

Paul Waldman: Why the Hyde Amendment is suddenly a Democratic primary issue

The Post’s View: The fact that Missouri only had one abortion clinic left was already a scandal

E.J. Dionne Jr.: Alabama shows we need a different abortion dialogue

Elly Lonon: I had an abortion. It’s none of your business why.