On Tuesday, Sen. Marco Rubio proposed a convention led by the states to create new amendments to the Constitution. We looked at this in 2014 when former Oklahoma senator Tom Coburn had a similar proposal. Since the political hurdles haven't changed, we're re-publishing this article now to explain why such an event is unlikely.

Sen. Tom Coburn (R-Okla.) is leaving his seat at the end of this Congress primarily due to his health. But that he'll be leaving at the end of perhaps the least productive Congress in modern history clearly hasn't escaped his notice. In an interview with The Hill, Coburn embraced an increasingly popular way to get around a Congress that isn't doing much: getting the states together to initiate a convention aimed at amending the United States Constitution.

There's clearly a kill-a-fly-with-a-hand-grenade aspect to this. The 113th Congress that will be Coburn's last has enacted 163 laws since January 2013 -- which, while low, is still about six times the number of constitutional amendments. That's because constitutional amendments were never intended to be a form of legislation; the Founding Fathers assumed Congress would do that to the public's satisfaction, or the public would elect a new Congress. That thinking may have been flawed. Control of the Senate might switch after November. Control of the House will not -- and nearly all of the House incumbents will return to Washington.

Coburn's goals -- as told to The Hill: "I think we ought to have a balanced budget amendment, I think we ought to have term limits. I think we ought to put a chokehold on regulation and re-establish the powers of the Congress." -- depend largely on Article V of the Constitution, the shortest of the document's seven articles. It establishes two ways in which the Constitution can be amended. First, two-thirds of the Senate and House can pass an amendment. Or, should Congress be incapable of passing even simple majority legislation, two-thirds of the states can request a constitutional convention to draft amendments.

It's this second plan that Coburn is endorsing. He's already reached out to two groups that are involved in an ongoing push to get state legislatures to make the appropriate request. One, Citizens for Self-Governance, has an ongoing project calling for a "Convention of States" with the goal of amending the Constitution. Its priorities, not coincidentally, echo Coburn's.

The thing about an Article V constitutional convention, though, is that it has never happened, so it's very unclear how such a gathering would be organized and run.

For example: Earlier this year, the state of Michigan joined several other states in calling for a convention to pass a federal balanced budget amendment. As was reported at the time, this spurred a cascading set of questions. Two-thirds of the states, the threshold necessary for a convention, comes to 34 states. And under one measure, Michigan became the 34th state to call for a convention on a balanced budget amendment, thanks to a push in the 1980s during which a number of other states made a similar demand. But some of the states rescinded those calls. And it's not clear if there's any sort of time limit that might apply to such requests.

Shortly after that Michigan vote, the non-partisan Congressional Research Service tried to answer some of those (many) questions. Or, more accurately, it tried to answer a much wider set of questions, to wit:

What constitutes a legitimate state application? Does Congress have discretion as to whether it must call a convention? What vehicle does it use to call a convention? Could a convention consider any issue, or must it be limited to a specific issue? Could a “runaway” convention propose amendments outside its mandate? Could Congress choose not to propose a convention-approved amendment to the states? What role would Congress have in defining a convention, including issues such as rules of procedure and voting, number and apportionment of delegates, funding and duration, service by Members of Congress, and other questions.

Unfortunately, the CRS couldn't offer clear answers to those questions -- answers that almost certainly would need to come from a judge at some level of government. It does, however, walk through existing thinking on possible responses, much of which conflicts. For example, the Michigan request might be the 34th, if no time limits apply to requests for a convention and if states can't rescind previous requests. Or it might be the 23rd, if states can rescind those requests. Or it might be the the seventh, if there's an admittedly arbitrary seven-year limit on requests.

Coburn and his allies appear to want to eliminate any doubt on the number of states making such requests. There exist separate organizations for legislators and toolkits for people to petition their legislators aimed at the same goal: reaching a 34-state margin that won't require a judge to sign off on a convention.

What the convention would address, though, would almost certainly be a contentious dispute. For example: California and Vermont both passed requests for a constitutional convention -- but on the topic of campaign finance, not a balanced budget amendment. Under most interpretations of Article V, those requests don't count toward the 34 states that Coburn hopes to cobble together. But if Coburn's cobbling is successful, could the convention suddenly branch out and pass an amendment repealing the Citizens United decision? That's the fourth question in the block of questions raised by the CRS, above. And its answer, in short: No idea. (In longer form, though: opinions vary, as outlined on pages 25 and 26.) In July, the Center on Budget and Policy Priorities offered its opinion. It quotes Supreme Court Justice Antonin Scalia: "I certainly would not want a constitutional convention. Whoa! Who knows what would come out of it?"

At Wikipedia, there's a lengthy list of times at which a state legislature has passed a call for such a convention -- but the margin has never been reached. There are numerous reasons for that, but one of the most telling is what happened when states called for the direct election of Senators. (Prior to the 17th Amendment, senators were elected by state legislatures.) By 1912, faced with calls for a constitutional convention from a wide swath of the existing states, Congress passed the new amendment and sent it to the states for ratification, which happened the next year. Like Scalia, Congress almost certainly didn't want to see a group of citizens get together and start proposing other amendments.

It's safe to assume that Congress would again intervene before a constitutional convention became a reality, for the same reason. So who knows. Tom Coburn might finally actually get Congress to act -- but only by leaving Congress and threatening to leverage the power of public opinion.