For what seems like the hundredth time since President Trump took office, Sen. Susan Collins is in a bind. Justice Anthony Kennedy’s retirement has provided Trump with the opportunity to appoint another conservative to the Supreme Court—provided he can manage to get one through a closely-divided Senate. And so the spotlight is once again fixed on Collins, whose support the nominee is likely to need.

This is nothing new for the Maine Republican, who has frequently found herself at the center of legislative controversies over the past two years, as the razor-thin Republican majority has tried to finesse Trump’s agenda through the Senate. At times, Collins has been instrumental in stymieing that agenda, as when she voted to spike Republican efforts to repeal Obamacare last July. And at times she has been instrumental in its success, as when she cast a critical vote in favor of the Republican tax bill in December.

While her decisions have varied, one thing has remained constant throughout: Collins has always worked to cast herself as a congenial, centrist influence on the process. This has sometimes led her to make head-scratching justifications. When she voted for the tax reform package, for example, Collins insisted she had pledged her support in return for a Republican guarantee to pass additional legislation to stabilize Obamacare insurance markets by the end of the year. Democrats complained that Collins had signed herself on in exchange for an empty promise, and they were right: Congress twice failed to pass the compromise bill.

Which brings us to Collins’ attempts to thread the Kennedy needle. The prospect of a solidly-conservative court has caused concern about the fate of every liberal’s favorite super-precedent, Roe v. Wade. Collins is a pro-choice Republican and she seemed to take a strong stand on Roe last Sunday, telling CNN’s Jake Tapper that she wanted “a nominee who would respect precedent” and that “I would not support a nominee who demonstrated hostility to Roe v. Wade,” which would indicate to her that “their judicial philosophy did not include a respect for established decisions, established law.”

This sounded like a line in the sand: No nominees who could endanger Roe. But more important is what Collins didn’t say: that she would require a potential nominee to demonstrate to her satisfaction that she would vote against overturning Roe. If this seems like a fine distinction, recall that Collins voted to confirm Neil Gorsuch despite the fact that he remained largely silent on Roe throughout his confirmation hearings—and that Trump repeatedly pledged on the campaign trail to nominate “pro-life justices” who would work to overturn the ruling.

When Tapper pressed her on this, Collins replied: “I had a very long conversation with Justice Gorsuch in my office, and he pointed out to me that he is a co-author of a whole book on precedent.” When it comes to his position on Roe, of course, this ultimately matters little: a judge can have a deep respect for precedent but still believe a particular case was decided incorrectly, an argument that pro-life conservatives have made about the abortion decision for decades.

If Collins is being evasive, it’s not hard to see why. The ideological gulf between liberals and conservatives is widest at the Supreme Court, where the two sides disagree not only on what decisions the court ought to reach, but on the very standards by which it ought to deliberate. For conservatives, who view the balancing mechanisms set up by America’s founders as essential to preserving liberty and thus good in themselves, a good justice is an originalist in the mold of Antonin Scalia: one who will seek carefully and dispassionately to deduce the meaning of laws passed by Congress, and whether they are in tension with the plain text of the Constitution as it was originally intended to function.

For their part, progressives see the role of government as being to redress the power imbalances that arise naturally in society. And by their lights, a slavish devotion to the political systems of a deeply prejudiced society—such as the America of 1800—is a deeply radical stance. Both sides see their own views on the Supreme Court as natural, moderate even, and view the other side as radical.

Which leaves Collins and other aspiring centrists in a difficult place. Because the centrist stands across their own ideological and procedural gulf from the progressives and the conservatives and Collins is being forced to make a decision that, by centrists' own lights, she shouldn't have to make. Thirty years ago, before Democrats turned the Senate's advise and consent function on the Supreme Court into another front on the culture war, centrist senators merely had to cast judgment on a nominee's basic competence and fitness for office. Now Senator Collins is tasked with deciding the fate of Roe by proxy, a burden which should not, by any reasonable understanding of the Constitution, be hers to bear: She is a single senator in one house of a bicameral legislature, not a philosopher-king. Viewed through that lens, it's no wonder her reasoning sounds tortured from time to time.

It's enough to give you sympathy for the centrist.