The Republican debate on Tuesday evening was set for fireworks, but the first real explosions of the night came from an unexpected source.

A substantive debate on economics and tax policy descended into petty insults when Ohio Gov. John Kasich and Donald Trump squabbled over the issue of whether millions of undocumented immigrants in the United States could be deported.

Kasich, who interrupted the moderators multiple times throughout the debate to interject his views, rebutted the idea that a future President Trump could deport millions of immigrants after the construction of a border wall between the United States and Mexico.

“In 1986, Ronald Reagan basically said, the people who were here, if they were law-abiding, could stay,” Kasich said, citing the conservative icon.

Kasich then blasted Trump for making a “silly argument,” and added that the notion of deporting millions of people, including children, was “not an adult argument.”

The Ohio governor’s confrontation with Trump seemed to push the blustery tycoon off balance, and garnered some applause from the audience.

For his part, Trump pooh-poohed Kasich’s economic know-how, claiming that Ohio’s economy under the governor had only grown thanks to its oil resources, while he had built a billion-dollar empire for himself from scratch.

“I don’t need to hear from this man,” Trump said dismissively. “Let me tell you, you’re lucky in Ohio that you struck oil.”

After former Florida Governor Jeb Bush tried to jump into the conversation, Trump pivoted. “You should let Jeb speak,” Trump told Kasich.

It’s unclear whether Kasich’s interruptions will be seen by voters as assertive or rude. Kasich drew moderate support from the audience at the debate.

But a focus group in New Hampshire, led by pollster Frank Luntz, reacted poorly to the interjections.

The Real Clear Politics polling average for Kasich has him at 3 percent support nationwide. Trump, meanwhile, sits at the top of the field with 24.8 percent.