The oft-cited possibility of brokered conventions are akin to how Mark Twain once described the weather — lots of people talk about it, but hardly anyone does anything about it. With four candidates in the Republican presidential race, the potential for the leading candidate failing to reach the required number of delegates bound for the first ballot is higher than it has been for decades … which is not to say that it’s necessarily a likely outcome. Even if the leading candidate gets a narrow majority, however, that may not mean they will prevail on a first ballot, John Fund argues today at NRO — and if it’s Donald Trump and he has not released his tax returns by the RNC convention, Fund writes, delegates should abstain rather than enter their vote for him.

More than a year after first promising to do so, Trump has yet to release that information. Fund writes that delegates should take Ronald Reagan’s advice to “trust but verify” before putting the GOP at risk in a general election with a candidate lacking that basic level of vetting:

A political party that didn’t demand the public release of Donald Trump’s tax returns could be committing electoral suicide. In his 40-year business career, he has assembled an empire of great complexity along with a serial record of credibility problems. In other words, he often “makes stuff up.” This is a man who said, under oath, in a 2008 libel suit he later lost: “My net worth fluctuates, and it goes up and down with the markets and with attitudes and with feelings, even my own feelings.”

The federal candidate financial-disclosure forms Trump points reporters to are not audited for accuracy or completeness.

Republican voters, GOP officials, and all Americans should demand that Donald Trump release his tax returns, something he refuses to do with the flimsiest of excuses. If he doesn’t release them, no one should be surprised if a leak of the juiciest details comes from the Obama administration before the November election. And the odds that anyone in the government would pay a penalty for that? Ask Lois Lerner, the comfortably retired former IRS official at the heart of the scandal involving discrimination against conservative non-profit groups.

If not, delegates to the convention in Cleveland should impose some accountability … by walking with their feet. And thanks to the lack of ground organization in the Trump campaign, he’s uniquely vulnerable to this method:

If Donald Trump won’t release his tax returns prior to the GOP convention, the delegates pledged to him on the first ballot should abstain from giving him their votes. Other than their vote not counting, there are no realistic consequences for any delegate doing so on the first ballot. A few states make breaking the first-ballot pledge rule a misdemeanor, but no one is ever prosecuted. In theory, state leaders could exact political retribution but such discipline is rarely exercised. …

Here’s how one Republican strategist explained the situation in his state: Donald Trump won the February 20 South Carolina primary with 32 percent of the vote but because he carried every congressional district, he won all 50 delegates. But as in almost all states, no actual people have been chosen to fill those slots yet. “There are mostly phantom delegates,” argues Elaine Kamarck, a Brookings Institution scholar and author of The Primary Games. “Understanding this is critical to understanding why this wild election year may get wilder still.” She writes that it is unclear what “would actually happen on the floor of the convention if some Trump delegates decided to vote for someone else.” But the Republican convention experts I talked to largely argued that if a delegate and his or her alternate chose not to vote, Trump would receive one fewer vote.

An RNC official on background confirmed this, but also noted that each abstention would lower the number of delegates needed to win, too; the rules specify that the majority applies to delegates actually voting, not merely assigned. On top of that, each delegate has an alternate that could be asked to vote in stead of an abstaining delegate, with the exception of the 168 delegates representing state party officials. Still, if the number of bound delegates Trump had was only barely a majority coming into convention, enough abstentions could eliminate Trump’s majority and throw the vote to a second ballot, where most states allow for delegates to vote for whichever candidate they prefer rather than reflect the vote total.

Under normal circumstances, this wouldn’t put a candidate at much risk, because they would have worked the local precincts to make sure their supporters moved forward in the state-convention process. Trump, however, has not invested in that kind of effort. Ron Paul’s grassroots organization actually flipped this equation by beating Mitt Romney and Rick Santorum in some caucus states (Iowa most famously, but also Minnesota and a few others) to disrupt the nomination process and vote for Paul in Miami four years ago.

Just because this can happen doesn’t necessarily mean it will, or even that it should. The larger the majority Trump wins in the field, the less likely that this would take place. But even if Trump gets 1237 or just a handful over that, a few delegates might not want to incur the wrath of hundreds of Trump supporters in the room with a floor stunt. Furthermore, if Trump comes in with hundreds more delegates than Ted Cruz or Marco Rubio, then what is the rationale for denying the nomination to someone who clearly outperformed all of the other Republican candidates — and why should Trump’s supporters stick with the GOP after such a move? That risks a surgery that kills the patient more quickly perhaps than the disease.

Still, it’s worth watching as one potential threat to the process. And if Trump doesn’t get a majority before the convention, it may indicate that he never will.