There would be significant political pressure put on GOP senators to confirm the selections of a GOP President. Regardless of how awful they might be.
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As opposed to a straight party line vote for the liberal activists that Hillary or Obama would nominate. Republicans won’t control the Senate next term. There are only 12 or 13 Democratic Senate seats in play. 23 or some such for Republicans and only a few of those are safe. So the Dems will have the Senate and rubber stamp any Clinton nomination. A moderate like Kennedy or O’Connor is a lot better than a Ruth Bader Ginsberg. A LOT better and likely what a McCain will nominate. Those moderates might even be swung right when they reach the court and interact with Robertson, Alito, Scalia and Thomas. And these next Justices are likely to be on the court for 30, 40, and possibly even 50 years if a jurist in their early 40’s is nominated. It’s a critical difference.
“Republicans won’t control the Senate next term.”
So long as they have enough to successfully fillibuster, it doesn’t really matter. Although the GOP might find itself with less than that number.