CLEVELAND, Ohio -- Donald Trump is Donald Trump, and he didn’t have to raise his hand or insult Rosie O’Donnell again to prove it.

But the most meaningful and perhaps lasting action of the first Republican debate was occurring around him. The fault lines that are likely to define the battle for the GOP nomination were on full and sometimes awkward display Thursday night.

Imagining a field that does not include Trump’s zingers reveals soft spots and hard edges inside the Republican field.

To Trump’s left was another frontrunner -– Jeb Bush -– looking anything but comfortable in the spotlight. He broke with party dogma on immigration, got booed on his education stance, continued to struggle with questions of political dynasty, and was again left explaining his position on Iraq.

“I’m going to have to earn this,” Bush said, speaking truthfully.

To his right was Scott Walker, hastily explaining positions on immigration and abortion in his first real exposure of this magnitude.

Rand Paul and Chris Christie sparred over national security tactics -– in an exchange that turned hot in a hurry, complete with an eye roll, raised voices, and arguments about who’s hugging whom and why.

Boosted by a hometown crowd, John Kasich offered a more uplifting vision than most of his rivals. It’s worth remembering from his party’s perspective that he defended both his attendance at a gay wedding and his decision to expand Medicaid -- even while explaining the appeal of Donald Trump.

Some of the other candidates seemed to disappear for stretches of the debate, whether by design of the questioning’s pace, or other circumstances.

Over time, steady performances by candidates including Marco Rubio and Ben Carson could be rewarded by voters, though were hardly memorable at the outset of debate season.

Beyond Trump, the forum served as a barometer of how far the other major contenders have to go to convince the party base they’re worth betting on – and to hash out the divisions that have defined the Republican Party in recent years.

Late in the debate, Bush used Trump to find a better groove -– offering a path for his party through the cloud of The Donald when he declined to directly engage him after an attack on his brother’s presidency.

“Mr. Trump’s language is divisive,” he said. “We’re going to win when we unite people with a hopeful and optimistic message.”

But Trump knows his audience, and knows how to fill gaps in a, well, huge field.

“Our leaders are stupid. Our politicians are stupid,” he said.

It’s a harsher message than the field deserves. But the first debate was hardly edifying, and was the opposite of clarifying. The celebrated deep bench may need seasoning – and will get it in the picked-up pace of debates from here.