Wisconsin Gov. Scott Walker called out real estate mogul Donald Trump at the second GOP debate Wednesday night. Walker's comment that "we don't need an apprentice in the White House -- we have one right now" made an instant splash on social media, with hundreds of people posting messages that propelled the phrase to a trending topic within minutes.

Walker took aim at Trump, famous for hosting the reality game show "The Apprentice" from 2004 through this year, shortly after the debate kicked off Wednesday night. After the zinger, Walker likened Trump to President Barack Obama. "He told us all the things we wanted to hear in 2008," he said. "We don't know who you are or where you're going. We need someone who can actually get the job done."

Trump interrupted him then, and the two candidates attempted to talk over each other. Trump could finally be heard saying, "In Wisconsin, you're losing $2.2 billion right now. I would be so much better than that." Twitter lit up, mostly with tweets teasing Walker for what they said sounded like a pre-written statement.

Going into Wednesday's 8 p.m. primetime debate, held by CNN at the Ronald Reagan Presidential Library in Simi Valley, California, Walker was trailing in the polls. He had dropped from 10 percent support among Republican primary voters in August to 2 percent, according to a CBS News/New York Times survey. Walker was only beating former Texas Gov. Rick Perry, New Jersey Gov. Chris Christie, former Pennsylvania Sen. Rick Santorum, Louisiana Gov. Bobby Jindal, former New York Gov. George Pataki, South Carolina Sen. Lindsey Graham and former Virginia Gov. Jim Gilmore -- most of whom were just invited to the "kiddie table" pre-debate at 6 p.m.

An anonymous Walker aide told NBC News before the event that he planned to "inject himself" and "mix it up" on Wednesday. During the first debate last month, the Wisconsin governor came in second-to-last place for speaking times. He talked for 5 minutes and 43 seconds, ahead of Sen. Rand Paul, R-Ky., at 4:51. Trump was No. 1 on the list, speaking for more than 10 minutes.

Outlets like Politico named Wednesday's debate his "last best chance" to save his campaign, which faltered after the first in which he was largely passive and called himself "aggressively normal." This time, Walker told CNN he planned to be more assertive and "make the case that we're ready to wreak havoc on Washington," capitalizing on the anti-insider rhetoric that's buoyed Trump, neurosurgeon Ben Carson and former CEO Carly Fiorina's campaigns.

The next debate was set for Oct. 28.