We're back in government shutdown territory this week, with the deadline looming at the end of this week. This is always an unpleasant moment, and Sen. Rob Portman, R-Ohio, along with a motley assortment of moderate and conservative Republicans, has a proposal that would avoid the all-too-common shutdown-showdown by putting appropriations into autopilot mode for a few months after each government shutdown deadline is met.

"Almost everybody hates government shutdowns. They don't accomplish anything. They don't get our fiscal house in order and they disrupt critical government programs that have a big impact on people's lives," Portman said in a statement provided to Roll Call ahead of the Senate reconvening Monday....The bill would provide automatic, flat-line continuing appropriations for 120 days, followed by further continuing spending with a one-percent reduction every 90 days after that.

I'm not sure this is the exact formula for success, but something has to give eventually. Otherwise, it simply will give, thanks to the precedent that former Senate Leader Harry Reid created when he changed Senate rules in 2013 with a simple majority vote.

Which is to say, if we don't get a change on appropriations soon, then we're probably going to get the nuclear option for appropriations bills before long.

Here's why I think it will happen: Appropriations bills, like reconciliation bills, have a special status in parliamentary procedure and lower stakes (from one perspective, anyway) in terms of what they contain. And this fact will be used as an argument to justify the change.

Not that it is necessarily justifiable, but the fact that spending bills are different will surely help proponents argue that they are still not sending the Senate further down a slippery slope. (This is, of course, characteristic of the arguments you hear on your way down a slippery slope, but....)

First, appropriations bills are temporary. They fund the government for a set period of time — ideally for a full fiscal year, often for shorter periods in recent years. Whatever Congress does through appropriations is not lasting and must be re-done the following year or will vanish by default. Therefore, the supermajority requirement could be viewed as less urgent, given the transient nature of appropriations.

Second, appropriations bills cannot create new policy the way regular bills can. Without meeting one of the separate supermajority requirements not related to the filibuster (which would presumably be kept in place — for now?), they cannot create or fund programs that haven't been authorized already, nor can they contain provisions that are not germane to the bill's subject matter or which "change existing law," nor can they exceed the spending limits set in the budget resolution (which passes with a simple majority vote).

The closest that appropriations bills can come to making policy are riders, typically taking the form, "no funds authorized or appropriated by this bill shall be used for such-and-such." (Even this application has limits on how it can be used.) But even here, the power to make policy in an appropriations bill is a negative power. "We won't fund this particular thing" isn't the end of the world for anyone the same way as, say, a major change to the Medicaid program might be (which like other entitlements isn't subject to the annual appropriations process), or reform of federal labor laws, or a ban on gun ownership, or what have you.

In short, as with reconciliation bills, there's less at stake with respect to what passes than there is with the average controversial bill that would make big, permanent changes to the federal code. But there's a lot more at stake with respect to what happens if no appropriations pass at all — namely, a government shutdown.

This is why we're probably headed — maybe not now under Senate Majority Leader McConnell, but at some point soon — toward a nuclear confrontation to prevent government shutdowns for good. A bill like Portman's could stave off that day. Democrats are unlikely to support something that ratchets spending down (even slightly) over time as a consequence of Congress failing to pass anything, so this bill may not do the trick. But something like it is probably needed.

Perhaps a true Senate rule change, performed with the required two-thirds vote, would be more appropriate. The bipartisan creation of a separate process of appropriations bills might actually restore some legitimacy to Senate procedure, and get Congress back to the point where regular-order appropriations are the rule rather than the exception.