Nothing unifies the Right more than the idea that this president should appoint conservative judges. The border wall, the Muslim ban, trade wars, Putinphilia: All of these issues divide the coalition that got Trump elected to one extent or another. The list unites it.
Of course, if you’re a liberal, uniting the Right is hardly a priority. But the simple fact is that any potential nominee who could conceivably win even a handful of Democratic senators would be a betrayal of Trump’s most important campaign promise and would cost him far more in Republican support.
If Trump were to nominate an obviously solid conservative not on the list, conservatives would probably live with it, but it would be a needless breach of trust with Republicans that would earn nothing from Democrats. Meanwhile, if he were to name some “bipartisan” liberal judge, the conservative backlash against George W. Bush after his nomination of Harriet Miers would seem like a polite disagreement over a game of bridge at the old-age home by comparison.