Seven months ago, after he signed a pledge to support whoever won the GOP nomination, Donald Trump said, “I see no circumstances under which I would tear up that pledge.”

That was then. Today we see a different Trump. On Sunday, he told Chris Wallace of Fox News that while he wanted “to run as a Republican,” he wouldn’t rule out an independent or third-party race this fall. “We’re going to have to see how I was treated,” he warned.

GOP leaders should have known better than to have taken his pledge seriously. As the Associated Press pointed out in September 2015, his record on honoring contracts is at best spotty:

When lender Boston Safe Deposit & Trust refused to extend the mortgage on his Palm Beach resort, Mar-a-Lago, he ceased making loan payments until the bank capitulated in 1992.

In his book The Art of the Comeback, Trump proudly recounts forcing his unpaid lenders to choose between fighting him in bankruptcy court or cutting him an additional $65 million check. Afraid of losing their jobs, the bankers folded, Trump says.

Reince Priebus, the chair of the Republican National Committee, has dismissed the chance of a Trump independent bid as “posturing.” Robert Eno of Conservative Review noted last week that Trump could be kept off many state ballots by “sore loser” laws that bar a candidate who has run in a partisan primary from running in another party in a general election. “If Trump were to wait until after the Republican National Convention to declare an independent candidacy, he could only compete for a maximum of 255 electoral votes,” Emo concluded. “This means he cannot win the presidency were he to wait until after [the] convention to run an independent bid.”

But many Republicans worry that Trump could still play “spoiler” by merely threatening to run an independent campaign. “Sore loser laws don’t hold up well in court,” says Richard Winger, the editor of Ballot Access News. “They also aren’t easily enforced. John Anderson ran as an independent in all 50 states in 1980 after ending his Republican campaign, and not one of the sore-loser laws was enforced against him.” Even if they were enforced, Trump could easily evade them. Winger says it would be easy to put Donald Trump Jr., the real-estate mogul’s son, on state ballots and make it known that if the Trump ticket won a state, its pro-Trump electors would in reality be voting for the elder Trump.

It’s true that deadlines for collecting ballot signatures in several states will have passed by the time the GOP convention begins, but a man of Trump’s wealth could probably rent a ballot line on many states from several smaller parties that are already on the ballot. “In at least 13 states, parties ranging from Reform to American Independent could nominate Trump and give him a ballot position,” Winger says.

Of course, in such a scenario, Trump would know that he probably wouldn’t win a majority of the Electoral College. And by making it more likely that Hillary Clinton or another Democrat would win key swing states such as Virginia and Florida, he would destroy the Republican nominee’s chance of winning the White House.

Trump may indeed be bluffing about an independent candidacy, and RNC Chairman Priebus seems to think so. “Some candidates think that, you know, there’s leverage to be had over making these kinds of statements,” Priebus told ABC’s This Week today. “There’s no leverage over us. We’re going to administer the convention the same way. And if the candidate can get to a majority on their own, then they’re going to be the nominee. But no amount of leverage and statements are going to change it.”

Priebus went on to say that every GOP candidate had signed pledges to support the nominee in exchange for access to the RNC’s valuable voter data and registration lists. But raising that issue is probably a futile talking point.

The real issue is how Priebus and his fellow GOP leaders will respond to the Trumpian squeeze plays. Already, Trump ally Roger Stone is warning that “Trump Nation” will organize “days of rage” at the GOP convention if their man is treated unfairly. “Days of rage” is a historic reference to the riots that broke out at the Democratic National Convention in Chicago in 1968.

As Donald Trump piles up more rookie campaign mistakes and his momentum stalls, he is clearly developing a Plan B for the Cleveland convention. Call it “The Art of Intimidation.” Republican leaders shouldn’t twist convention rules in Cleveland to block Trump’s nomination. Nor should they disrespect his voters. But they also should call out the veiled threats from Team Trump for what they are: a form of political blackmail. And no party seeking a mandate to govern should surrender to such lowball tactics.