A bunch of folks have already taken solid whacks at the absurd news that a bipartisan group of 64 Senators — divided exactly evenly between Dems and Republicans! — has written a letter to President Obama demanding that he lead bipartisan discussions on how to rein in the deficit.

As both Steve Benen and Matthew Yglesias rightly note, there is nothing stopping these Senators — who constitute a majority of the upper chamber — from reaching their own conclusions on what needs to be done. But they haven’t suggested anything in concrete policy terms. Instead, they are simply demanding that Obama show leadership by stepping in and compensating for their own lack of leadership.

But I wanted to flag another aspect of their letter: The peculiar definition of “bipartisanship” it embodies.

Note that the letter defines the parameters of the discussions senators want Obama to lead as follows:

We urge you to engage in a broader discussion about a comprehensive defict reduction package. Specifically, we hope that the discussion includes discretionary spending cuts, entitlement changes, and tax reform.

I checked in with a couple of Senate aides about this, and they were amused by the reference to “tax reform.” As they put it to me, this is a weaselly and euphemistic way of suggesting that maybe, just maybe, tax hikes on the rich (which many Dems want) should possibly be part of the discussions — without saying so outright in a way that Republican senators who signed the letter would find unacceptable.

By contrast, the first two of those, “discretionary spending cuts” and “entitlement changes,” are clear and direct references to the solutions advocated most emphatically by many Republicans and conservatives.

Everyone seems to want broad bipartisan discussions to take place on reining in the deficit. But it’s unclear whether Republicans will ever permit tax hikes on the rich — one of the leading solutions advocated by Democrats — to be even part of these bipartisan discussions. To be sure, the recommendations by Obama’s Fiscal Commission, which are the starting point for these discussions, recommended revenue increases, and the so-called “Gang of Six,” a smaller bipartisan grooup of senators, are also said to be entertaining tax hikes as part of their talks on the deficit.

But no one knows what this even means, or whether there’s any realistic chance that Republicans will ever agree to any such tax hikes as part of a broader deal. Until we hear otherwise, we should simply assume that Republicans will never find any tax hikes acceptable. Meanwhile, it’s simply assumed that “entitlement reform” could win the support of Democrats.

It’s a peculiar definition of “bipartisanship.”

UPDATE: And of course it should be added that the Fiscal Commission’s recommendations, such as they were, didn’t even pass the commission.