If Alito and Roberts make some blatantly un-constitutional ruling, like...

...establishment of religion, is it prima facia evidence for impeachment?

Can the type of rulings they make in itself be grounds for impeachment, or does the fact they sit on the Supreme Court make THEIR interpretation of what's constitutional the only thing that matters?

What happens if there is a clear disconnect between what the constitution actually says, and what Alito and Roberts rule?

Could they get away with ruling that the established religion of the United States is Christianity?

We've seen how little impeachment can relate to actual wrongdoing. Seems to me it works both ways, that a politically favored person can be immune from impeachment regardless of actual fault or culpability.

the Federal courts to the Supreme Court

...you'd not only need a simple majority in the House, but you'd need 67 votes in the Senate.

As far as I know, even if the Democrats won every single Senate race this November (a near-impossibility) they'd still have less than 60 votes. You'd need a significant breakaway among conservative Republicans for the purpose of removing judges who would represent their philosophy and replacing them with judges who didn't.

In other words, not a chance unless there's such a realignment that Democrats can virtually sweep the Senate races in both 2006 and 2008. Until that point, we're stuck with who we've got.

:-(

He gave the Christian Reich the heads-up that he would "remember the trust" they had placed in him, thus destroying the impartiality in his jurisprudence.

Get that nut off the bench.

...that wouldn't retroactively overturn their decisions.

And here's the irony: if they made such "blatantly un-constitutional" rulings, the only way those could be overturned judicially is if a future court were to overturn it. However, one of the general judicial principles on which the United States is founded (you know, the ones that progressives and Democrats respect while "strict constructionist" Republicans disregard at will) is that prior Supreme Court decisions determine precedent which is to be respected throughout the judicial system, even by future Supreme Courts. In other words, a Supreme Court decision about what is or is not constitutional is as firmly based as the Constitution itself, and can only be overturned by a new constitutional amendment. So, for a decision such as you mention above, the only chance we would have to correct it other than running a new amendment through the multi-decade process (and, remember, we couldn't even pass an amendment to guarantee women equal rights!) or going the as-yet untried Constitutional Convention route would be to find liberal Democratic appointees who are every bit as unscrupulous as Scalia, Thomas, Roberts, and Alito.

whatever five justices of the Supreme Court say it says.

If five justices interpret the 21st Amendment (ending Prohibition) to mean that red socks can only be worn on Sunday, then that's what the Constitution says.