Republican candidates in Tuesday night's Fox Business Network/Wall Street Journal debate will have their last chance for a debate game-changer until mid-December. 

Click here for live full coverage of tonight's debate on Fox Business Network.

And the high stakes are evident. 

The prelude to the Milwaukee face-off has been marked by tense sparring within the field's top tiers. The eight candidates on stage for the prime-time event, after spending the last debate bickering with the moderators, seem ready to get back to the issues -- and each others' history -- Tuesday night. 

Ahead of the fourth GOP debate, billionaire businessman Donald Trump released a policy paper focusing on U.S.-China relations, one of his hallmark issues. And he used an Illinois rally the night before to hammer rival Ben Carson over violent incidents during his youth. 

"This is a strange election, isn't it? ... This is the only election in history where you're better off if you stab somebody," Trump said. 

Carson, for his part, has spent the last several days sparring with the media and his rivals over reports questioning his personal story. 

"I am trying to move on," Carson told Fox News. But his campaign manager also says Carson will punch back if an opponent challenges him on stage Tuesday night -- suggesting a departure for Carson from past debates, where he mostly avoided the fray. 

The prime-time debate will be held at 9 p.m. ET, from Milwaukee, preceded by an earlier 7 p.m. ET debate with lower-polling candidates. It is expected to focus on economic issues, and is the last GOP debate until Dec. 15. 

Several candidates, including Florida Sen. Marco Rubio and former HP CEO Carly Fiorina, have used the debates to raise their profiles in the race while others have suffered in the polls following lackluster performances. 

This is the first time that just eight candidates will be on the main stage, a change that could give the contenders more time to explain their positions and engage each other. 

Rubio, in the hours before the debate, launched a striking ad against GOP rival Jeb Bush, the former Florida governor. The ad plays clips of Bush, before the 2016 campaign, praising Rubio. 

"I'm a huge Marco fan," Bush says in one clip. In another, he says, "He's probably the most articulate conservative on the scene today." 

The text of the ad blares: "Jeb Bush before his phony attacks." 

Bush, the former front-runner, has struggled in every debate so far, and Rubio is no doubt angling for the edge against him in Tuesday's showdown. At the last debate, Rubio deftly parried a critique by Bush of his Senate absences. 

The prime-time debate is set to include: Trump; Carson; Rubio; Texas Sen. Ted Cruz; Bush; Fiorina; Ohio Gov. John Kasich; and Kentucky Sen. Rand Paul. 

The candidates set for the earlier debate are: New Jersey Gov. Chris Christie; former Arkansas Gov. Mike Huckabee; Louisiana Gov. Bobby Jindal; and former Pennsylvania Sen. Rick Santorum. 

Rubio is currently third in most national polls, followed closely by Cruz, who by many accounts had the stand-out moment in the last debate by slamming the CNBC moderators for allegedly unfair and off-topic questions. Speaking with Fox News on Monday, Rubio said the polls have been "up and down," but "what I'm going to do is I'm going to focus on the message of my campaign." 

Still tangling for the lead are Carson and Trump. 

Speaking with Fox News, Trump pointed to the most recent polling in saying he's back on top. 

"I'm No. 1 in the polls, as you know, in every single -- I think I'm No. 1 in every single state. I'm now No. 1 again in Iowa. I had lost Iowa for a period of time, and I didn't quite understand it," Trump said. 

Trump has shown no hesitation about going after Carson, for everything from his past writings about having anger issues growing up, to stories questioning elements of his personal narrative, to Carson's statement that Egypt's pyramids were built by the biblical Joseph to store grain. 

"He's having a hard time. The pyramids are solid structures. You can't put grain in the pyramids because they're solid structures," Trump said. 

Trump, who hosted "Saturday Night Live" over the weekend, also made headlines overnight by suggesting a "boycott" against Starbucks over its holiday cups that are missing winter or Christmas scenes. But then Trump added, "Seriously, I don't care."