WASHINGTON -- Tuesday's latest Republican debate put an exclamation mark on Jeb Bush's growing frustration with Donald Trump in the clearest sign yet that the former Florida governor is willing to be Trump's chief critic.
"So Donald, you know, is great at the one-liners, but he's a chaos candidate," Bush said in the debate. "And he'd be a chaos president."
Bush's frustration with the billionaire businessman is nothing new after Trump successfully branded Bush as "low-energy" early in the race -- a knock that has continued to dog the former Florida governor in public perception of his campaign.
But the Tuesday night debate showed Bush embracing the attack role even after joking just last week with New Hampshire voters that he was trying not to say Trump's name and expressing exasperation at the press' repeated Trump-focused inquires.
"There's no debate that Jeb Bush had his best performance last night, that he did a great job, that he was on the offense against Donald Trump," said Republican strategist Nicolle Wallace. "The unfortunate piece of it is many wonder and suspect that it may be too late."
Bush's attacks focus primarily on Trump's seriousness as a candidate and drawing a contrast with his own policy proposals -- frequently citing forethought in unveiling a strategy to confront ISIS earlier this year before it became a trending topic.
"It was a commander and chief debate in many ways," Bush said in assessing the debate on MSNBC. "I don't know if the front running candidate fared that well in that kind of context."
None of the Republican candidates have pledged not to support Trump if he ultimately becomes the party's nominee, but Bush has maintained the position that Trump will not reach nominee status.
"His policies aren't serious proposals, and he didn't offer anything compelling in response to that," Bush said in the MSNBC interview. "I offered, as did other candidates, significant, detailed proposals to protect the homeland."
As the candidate went after Trump on the stage in Las Vegas, his campaign was ready with supporting evidence, quickly distributing video clips of Trump's past comments via social media.
One of Bush's more memorable attacks on Trump went after comments the frontrunner made to Chuck Todd on Meet the Press earlier this year about getting foreign policy advice from "the shows."
Tuesday's performance comes as Bush has fallen to the middle of the Republican pack in the most recent polls -- something Trump was quick to point out during Bush's attack -- but a position Bush continually shirks off as unimportant political process.
"Well, let's see. I'm at 42, and you're at 3. So, so far, I'm doing better," Trump said.
This article first appeared on NBCNews.com.