From today’s rally in Iowa:

Sen. Marco Rubio of Florida said this week he supports the idea of a convention of states to amend the U.S. Constitution, adding a high-profile voice to an issue that has picked up renewed interest in some conservative circles.

“One of the things I’m going to do on my first day in office: I will announce that I am a supporter, and as president I will put the weight of the presidency behind a constitutional convention of the states so we can pass term limits on members of Congress and the Supreme Court and so we can pass a balanced budget amendment,” Mr. Rubio said in Iowa.

Would any Republican presidential candidate oppose an Article V convention if asked about it, especially if it was limited to congressional term limits and balancing the budget, as Rubio suggests? It’s a classic conservative (and now populist) litmus test: If you don’t support a convention, that must mean you support the status quo. How could anyone support this status quo? We’re nearly $19 trillion in debt and disgust at the political class is so high that the guy from “The Apprentice” might be elected president. Nothing could be more establishment than saying to the idea of a convention, “Nah, I’m fine with where we are right now.” At this point, as Bill Murray said at the end of “Groundhog Day,” anything different is good.

Or is it? The last time Rubio mentioned a convention, he said he was open to the idea but sounded a note of caution:

“Just make sure that we know how it is going to turn out because if you open up the Constitution, you are also opening it up to people that want to reexamine the First Amendment, people who that want to reexamine the Second Amendment, people that want to reexamine some other fundamental protects that are built into the constitution,” the 44-year-old said.

“But ultimately there is a provision that exists for citizens to amend their Constitution and reexamine it, and if our citizens want to do that, I will be supportive of it,” he said. “But just be aware that the same groups that are trying to pass legislation that violates the Constitution are the same groups of people that are going to try to change that Constitution, and we are going to fight them at that convention.”

Help me with the math here. To call a convention, you need 34 states to agree; to ratify new amendments at that convention, you need 38 states. Mitt Romney won 24 states in 2012. Even in a best-case scenario in 2016 for the GOP, you’re probably looking at 20 solidly blue states, which means you’re four short of what you need to call the convention and eight short of what you need to actually get things passed. On the one hand, that daunting math should calm fears of liberals going nuts at a convention and repealing the Second Amendment, carving out exceptions to the First, and so on. Even if they can find 30 blue states to support that, they’d still need eight red ones to join them in order to enact the proposals. Not going to happen. The only ideas that stand a chance of passing are procedural reforms that enjoy broad bipartisan support, like term limits for Congress.

On the other hand, apart from term limits, how many other reforms enjoy such sweeping cross-partisan enthusiasm that blue states would not only agree to join a constitutional convention aimed at them but to help conservatives pass them? If you think the left is going to go for a balanced-budget amendment, I fear you’re kidding yourself. The BBA may poll well in the abstract, but wait until the media starts digging into it and Democrats start shrieking about conservatives’ “evil scheme” to destroy Medicare by capping federal expenditures at revenue levels. A balanced-budget amendment is about restraining the power of the federal government to grease special interests by spending beyond its means. Why on earth would the modern Democratic Party agree to something like that?

Either you’re going to have to severely lower expectations for a convention — term limits might be the only thing that passes — or you’re going to have to horse-trade with the left to get things on the agenda. For instance, you might suspect that blue states, under the hot spotlight of an Article V huddle, would be more reluctant to vote no on a BBA than they would under the traditional mechanism where Congress passes an amendment and then each state gets to quietly decide whether to ratify it or not. That, to me, is one of the great virtues of a convention over the traditional amendment process: The intense public attention means there’s nowhere to hide on extremely tough votes. (The other great virtue is that it removes Congress from the amendment process, making something like congressional term limits more viable.) But again, the left has some leverage here. If you want a vote on a BBA, which will probably fail anyway, they might insist on a vote on, say, a very limited exception to the First Amendment to cap the amount of money individuals can legally donate to candidates and their Super PACs. That’d be a tough vote for some red states given the brisk business Trump has done this year attacking the competition as bought-and-sold puppets of the donor class. Are you willing to risk a carve out to the First Amendment for a shot at passing a balanced-budget amendment? If not, how do you get Democrats to the table on the latter without coming to the table yourself on the former?

And if it’s true that the only thing (or one of the very few things) that can pass at a constitutional convention is term limits for Congress, why not focus right now on trying to get that passed through the traditional amendment process? Congress might resist, but given the mood in the country towards D.C. and the specter of populist demagogues like Trump growing in power if reforms aren’t enacted, they might not resist as vigorously as everyone expects. In fact, that’d be a dynamite idea for Trump: Insist that the GOP Congress pass a term-limits amendment before the primaries are over or else, you hint, you might go third-party. Dare other candidates, starting with Hillary Clinton, to endorse or oppose the idea. He’ll get an instant poll bounce and a feather in his cap from having introduced the issue in a major way into the campaign. Even in a worst-case scenario, where Congress refuses to pass anything, you’ve exposed their corruption and self-interest by forcing them to take a position. Public interest in term limits will be stronger going forward. There are ways, I think, to make this happen even without a convention, if you have enough effort — and the right players pushing it.

Unrelated exit question via Morgen Richmond, picking up on this Rubio post from last night: If Rubio imagined the Gang of Eight bill as merely an opening offer to conservatives in the House, who he hoped would make the bill better, how come he never mentioned that in his final Senate floor speech about the bill that was aimed at Republican voters at the time?