This afternoon’s sprawling House budget debate is totally predictable, and this evening’s roll calls will be important only at the margins in explaining how fiscal policy might shift during the rest of the year.

Two super-liberal Democratic plans and one super-conservative GOP plan will be rejected overwhelmingly. So will a copy of the Senate plan, although how many House Democrats vote against it will offer a clue about where the party’s budgetary center of gravity is these days. And then the House will adopt the official GOP budget, the so-called Ryan plan, for achieve balance in a decade.

The suspense then will be how many on the majority side oppose it. The answer is probably fewer than the 10 who voted “no” on Ryan’s budget last year, but more than the four who opposed his first budget back in 2011. In other words, the House GOP looks very well organized for the debate ahead.

Still, the most important fiscal vote so far this year will come on one of the dozens of amendments that will be thrown at the budget plan to be considered in the Senate — a debate that Majority Leader Harry Reid signaled this morning will still happen before the spring recess is allowed to start, even if the current stall over the keep-the-government-running-for-six-months spending bill delays the budget resolution deliberations into the weekend.

The key amendment, being written by Ohio’s Rob Portman and some other Republicans, would call for an orderly and filibuster-proof debate later this year on both a tax code overhaul and new limits on entitlement spending. There’s no way such a reconciliation bill is going to become mandatory — because the GOP House and the Democratic Senate aren’t even going to try to merge their budget blueprints into a compromise resolution. Still, a symbolic Senate vote in favor of the idea could smooth the path toward the climactic budget deadline of the year.

That’s the point, sometime in July, when the debt ceiling will need to be raised above $16.4 trillion in order to ward off a government default. Leaders of the most fiscally conservative camp in the House GOP are pressing their leadership to once again condition the grant of new borrowing authority on significant new deficit reduction, which this time would be all about curbing the growth of Medicare, Social Security and Medicaid. Even the GOP hard-liners concede that sequestration has cut all that’s appropriate from the discretionary share of the budget.

President Barack Obama has said unequivocally that he won’t negotiate a budget deal while the debt limit is held hostage. He’s also made plain that his willingness to lead the Democrats to swallow significant entitlement cuts is conditioned on a revived willingness of the GOP to swallow a tax code simplification that raises revenue.  The Senate budget plan calls for generating $975 billion that way in the next decade. The president would probably be willing to accept half that as the price for an equivalent amount of entitlement restraint. That would allow all sides to take credit for another $1 trillion in red ink reduction.

Such horse-trading will be almost impossible unless there’s some kind of assurance that any deal would be put before the House and Senate for simple-majority ratification votes. That’s why at least a somewhat bipartisan show of support for the Portman amendment in coming days would be so important.

But for the idea to have much chance, the GOP would need to drop the adjective “revenue neutral” from the language describing the sort of tax bill that would deserve the benefits of the reconciliation process — a system designed, after all, only for legislation that aims to reduce the deficit.