when he writes “ if pressure could be put on Bush to nix Harriet Miers in lieu of Samuel Alito, then I suspect that, if circumstance opened the opportunity to appoint a Supreme Court justice, similar effective pressure could be put on Romney from conservatives.” Romney might be willing to take the political hit from conservative legal activist groups if he nominates a David Souter-type mystery meat Justice. He might even be willing to take the hit from right-leaning voters. What are they gonna do, vote for Democrat X in 2016? But if it is clear that a plurality of Republican Senators will oppose such a nomination quickly, loudly, and persistently, then the calculation changes. The ideological incentives for most of the Democrats would be to support such a Romney nomination as the best that they are going to get under a Republican President and work with moderate Senate Republicans whatever other Republican Senators the Romney administration can suborn to okay the nominee. The partisan incentives for the Democrats as a whole would be to stand aside and enjoy the Republican civil war (kinda what they did during the Miers controversy) or attack the nomination from a different angle as a way to politically weaken Romney. so if Romney can count on the mass of the Senate Republicans to insist on at least a John Roberts-style Justice and he can count on immediate and intense opposition for anything less, then he would politically be better off nominating a John Robert-type.
All this of course is working from the assumption that Romney would be totally cynical about who he nominated for the Supreme court. Maybe he wouldn’t be. I’m using the cynicism model as a worst case scenario on how Romney might deal with the political incentives of the judicial issue.