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

Three months before primary voting begins, the Republican contest remains crowded and unwieldly.

Trump, the real estate mogul, has dominated the GOP race for months, but was a less of a factor Wednesday night than in the previous two debates.

Carson, the soft-spoken retired neurosurgeon who came into the debate with a burst of momentum, stuck to his low-key style.

Texas Sen. Ted Cruz garnered applause when he criticized debate moderators for trying to stir up fights among candidates.