Their goal of Roe v. Wade reversal in sight, many Republicans have private second thoughts Trump may deliver the Roe reversal Republicans have pledged. But amid broad public support for legal abortion, it's the last thing many privately want.

Jonathan Turley | Opinion columnist

“I’m like a dog chasing cars, I wouldn’t know what to do if I caught one.” That famous line from the Joker in "The Dark Knight" could well be delivered by dozens of Republican senators this month. For decades, Republican politicians have run on pro-life platforms and promises to reverse Roe v. Wade with a pro-life majority on the Supreme Court. That mantra was picked up most recently by President Donald Trump, who pledged to supporters that overturning Roe v. Wade “will happen, automatically” because he would appoint only pro-life justices to the Supreme Court.

The problem for the Republican Party is that Trump could actually succeed with the nominee he announces Monday to replace retiring Justice Anthony Kennedy.

Many Republicans say privately it is the last thing they want to happen, given the potential for backlash in House and Senate elections that could turn on thin margins. Polls put public support for Roe v. Wade as high as 70 percent, with a majority opposing a nominee who wants to reverse it.

That includes many of those suburban moms critical to the Republican majority. Roe is approaching 50 years, but it is still driving our political debate. It is one thing to chase a court and another thing to catch one.

Trump didn't get the memo on abortion

The biggest concern in Washington is that Trump did not get the memo about sounding pro-life without actually being pro-life. One of the most fascinating aspects of the Trump administration is the remarkably high number of promises that Trump has actually kept. Voters are used to presidents discarding promises, or being unable to keep them, after they assume office.

Given his reputation for hyperbole and distortion, few really expected Trump to make good on many of his promises. Yet he has assembled an impressive record on deliverables, from tax cuts to drilling in the Arctic National Wildlife Refuge to dismantling Obamacare; from cracking down on illegal immigration and trade he calls unfair, to moving the U.S. Embassy to Jerusalem, to rolling back environmental and other regulations.

If Trump were to deliver on reversing Roe, he would have accomplished something that five Republican presidents, including Ronald Reagan, could not achieve for decades. In other words, Trump might just mean it, and that is precisely the problem for many senators.

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Republican senators such as Susan Collins and Lisa Murkowski support abortion rights, and Collins has said that a nominee who would overturn Roe v. Wade would "not be acceptable." The question is whether such members are as serious in guaranteeing the continuation of Roe as Trump has been in pursuing its end.

For his part, Trump has announced that he "probably won't" ask any nominee where he or she stand on the case. This would allow all sides to have plausible deniability, though virtually everyone on Trump’s list is believed to oppose the reasoning of Roe v. Wade. As a result, the only way for Collins to be sure about Roe v. Wade is to demand an express assurance that the decision will be preserved by the nominee. What she is likely to receive is the same meaningless mantra from nominees that they respect precedent and will keep an open mind.

Since 1973, Roe has been the perpetual motion machine of American politics. It is likely to remain so for the next 50 years — regardless of the nominee. Even if Trump’s nominee were to vote to overturn Roe, the new majority may find Chief Justice John Roberts a hard sell for a frontal attack on Roe as opposed to narrowing decisions along its edges.

Roberts is the ultimate institutionalist and might get sticker shock from the political price of directly overturning the decision. (Roberts broke from the conservative wing to save Obamacare in 2012 rather than disrupt heath care coverage across the nation.)

Political momentum for abortion rights

However, even if Roe were overturned, the political controversy would only shift to the states, where each state would vote on the availability of abortions. Most states would likely protect the right.

Indeed, in 2013 Ruth Bader Ginsburg surprised an audience at the University of Chicago by saying that Roe v. Wade may have been a mistake in such a sweeping form. She said the politics of the decision were not good for the pro-choice cause: “That was my concern, that the court had given opponents of access to abortion a target to aim at relentlessly. ... My criticism of Roe is that it seemed to have stopped the momentum that was on the side of change.”

That momentum would likely be regained by any reversal of Roe, given the overwhelming majority that supports the right. Indeed, Ginsburg’s comment might prove prophetic if Roe is kept barely alive by the court. On a political level, it might be better for pro-choice advocates to see the opinion overturned entirely rather than left effectively dead by a thousand paper cuts.

If Roe lives, even in a greatly reduced form, the right will continue to reside in the Supreme Court. If it is overturned, momentum will likely approach madness as an estimated 70 percent of the country move to recreate the right in their states.

That is the car that Republicans fear to catch.

Jonathan Turley, a member of USA TODAY's Board of Contributors, is the Shapiro Professor of Public Interest Law at George Washington University, where he teaches constitutional and tort law. Follow him on Twitter: @JonathanTurley