Maybe I'm being anal here (it won't be the first time), but is a filibuster not a filibuster until it is attempted to shut it off? The House has a cloture rule that automatically ends debate; the Senate has a cloture vote that allows for unlimited debate. Until someone tries to stop debate, it is just debate. Once an attempt to stop debate fails and debate continues, wouldn't that then become filibuster?
On point (2), if the Constitution's "advice and consent" language doesn't permit filibusters, then the filibuster of Abe Fortas in 1968 was unconstitutional. I've never heard anybody argue that.
I looked up Foras' brief bio on an on-line almanac site, and I think the differentiation is this: Fortas was already on the Supreme Court. The filibuster was on his appointment as Chief Justice.
I don't see why that should make any difference. The Senate was there using the same constitutional advice-and-consent power that is at work in the Estrada matter. If it's legally wrong to filibuster Estrada's appointment as circuit court judge, I do not see why the filibuster of Fortas's elevation was not equally illegal.
"Filibuster" isn't even a legal term. It doesn't appear in the Senate rules. It's a colloquial term. So there's no way to decide, as a legal matter, whether what has happened or is happening is accurately called a "filibuster."
But, whatever we call it, if the DemocRATs succeed in blocking Estrada's appointment, they will have successfully set a precedent (actually a further precedent, after Fortas) that, where a party is willing to use all its power, 60 Senate votes are needed for the confirmation of a judge. It's that (further) precedent that we ought to want to stop, and it seems to me a cloture vote is a way to try to stop it.