But as Slate's Dahlia Lithwick points out, it's possible that Ginsburg broke norms and said what she did because Trump is truly an unprecedented candidate, and because the Senate is in the midst of an unprecedented blockade of a Supreme Court nominee ― circumstances that could pose a threat to the judiciary itself.
"Senate consideration of a nominee under these circumstances is not fair to the president, the nominee or to the Senate itself," Grassley quoted Biden as saying, even referring to it as the "Biden rule".
He would be an underdog to be the nominee under these circumstances, although whether Mr. Santorum or a dark-horse candidate was the more likely alternative is another question.
So far, many prominent Republicans have refused to endorse Trump and some, such as former Florida governor Jeb Bush and Senator Ben Sasse of Nebraska, have made clear they will not vote for their party's nominee under any circumstances.
James C. Dobson, an influential conservative leader, noted Mr. McCain's role in the bipartisan Gang of 14 in his announcement that he could not support the lawmaker as the Republican nominee under any circumstances.
In the final compromise, three of the seven Bush judicial choices that Reid and Rove had discussed were approved by the Senate, and it was simultaneously agreed that senators could filibuster a nominee "under extraordinary circumstances" — somewhat vague language that has yet to be tested.
But Mr. McCain's participation in the agreement nonetheless angered a number of conservative leaders, among them James C. Dobson, who cited the Gang of 14 when he announced that he could not support the lawmaker as the Republican nominee under any circumstances.
In 1976, Gerald Ford was the Republican nominee in similarly inauspicious circumstances.
Ultimately, the two parties averted a larger confrontation by a gentlemen's agreement to filibuster judicial nominees under only the most egregious circumstances, as when a nominee is overly partisan or obviously unqualified.
The compromise moves three unqualified appeals court nominees one step closer to confirmation and lifetime tenure, while Democrats agreed to use the filibuster against judicial nominees only under "extraordinary" circumstances.
In 2005, the Gang of 14 -- seven Republican and seven Democratic senators -- agreed not to block judicial nominees except under "extraordinary circumstances".
