BOULDER, Colo. — Marco Rubio bid forcefully for control of the Republican Party’s establishment wing in Wednesday night’s third GOP debate, deflecting jabs from Jeb Bush, who desperately sought to right his floundering campaign.

Insurgent outsiders Donald Trump and Ben Carson defended the seriousness of their White House efforts, underscoring the two-track fight for the party’s presidential nomination. But in an economic policy focused debate, both at times faded to the background during the two-hour contest.

Rubio tangled early with Bush, his friend and fellow Floridian, who entered the debate in need of a strong performance to soothe his supporters’ anxiety. Bush targeted Rubio for his spotty voting record on Capitol Hill, signaling that he sees the Florida senator as the candidate most likely to block his political path.

“Marco, when you signed up for this, this was a 6-year term and you should be showing up for work,” said Bush, who was forced to slash campaign spending in response to slower fundraising. “You can campaign, or just resign and let someone else take the job.”

Rubio sharply dismissed Bush’s critique as a political ploy by a struggling candidate.

“The only reason you’re doing it is that we’re running for the same position and someone has convinced you that attacking me will help you,” he said.

Three months before primary voting begins, the Republican contest remains crowded and unwieldly. Yet the contours of the race have been clarified, with outsiders capitalizing on voter frustration with Washington and candidates with political experience hoping the race ultimately turns their way.

Trump, the brash real estate mogul, has dominated the Republican race for months, but was a less of a factor Wednesday night than in the previous two debates. He largely refrained from personal attacks on his rivals, which has been a signature of his campaign, even taking a light touch with Carson, who has overtaken him in recent Iowa polls.

Carson, the soft-spoken retired neurosurgeon who came into the debate with a burst of momentum, stuck to his low-key style. He sought to explain his vague tax policy, which he has compared to tithing, in which families donate the same portion of their income to their church regardless of how much they make. And he insisted he had no involvement with supplement maker Mannatech, although he acknowledged using its product and giving paid speeches for the company, which has faced a legal challenge over health claims for its products.

Carson said it was absurd to allege he’s connected to the company. “If someone put me on their home page, they did it without permission,” he said.

Trump bristled when asked by a debate moderator if his policy proposals, including building a wall along the U.S.-Mexico border and deporting everyone who is in the U.S. illegally, amounted to a “comic book” campaign. And he defended his record in the private sector despite having to declare bankruptcy, casting it as a business technique.

“I’ve used that to my advantage as a businessman,” Trump said. “I used the laws of the country to my benefit.”

Texas Sen. Ted Cruz has been circling Trump for months, seeking to position himself as the heir to the businessman’s supporters if he fades. While Cruz holds office in the U.S. Senate, he’s cast himself as anti-establishment and a thorn in the side of GOP leaders.

Cruz garnered enthusiastic applause when he criticized debate moderators for trying to stir up fights among the candidates, casting it as a sign of media bias against Republicans — a popular line with GOP voters.

The jumbled GOP field is a stark contrast to the Democratic contest, where Hillary Rodham Clinton is strengthening her front-runner status over Vermont Sen. Bernie Sanders. Campaigning in New Hampshire ahead of the GOP debate, Clinton said the Republican contests are like a “reality TV show but the cast of characters are out of touch with actual reality.”