With national Democrats essentially pulling the plug on help for his campaign, Murphy tried repeatedly to lash Rubio to Trump, the controversial Republican presidential nominee endorsed by Rubio. But Murphy also was accused of a misstep as he tried to display his knowledge on foreign policy, leading to a pointed clash over the situation in Syria.
Rubio, meanwhile, alternated between coolly deflecting Murphy's shots while ridiculing the congressman's focus on Trump and positions on issues like the U.S. embargo on Cuba.
"Basically, the answer to every question tonight by Congressman Murphy is 'Donald Trump,' " Rubio quipped after Murphy pivoted from a question about police brutality to invoke the GOP presidential candidate.
Murphy also hammered away at Rubio's poor attendance in the Senate while Rubio unsuccessfully battled Trump for the Republican presidential nomination.
"If you voted as much as you lied, you might actually be a decent senator," Murphy said in one exchange.
Held in Bailey Hall at Broward College, the debate marked one of Murphy's highest-profile chances to take on Rubio. Most polls have shown the incumbent with a modest edge, usually inside the margin of error, though one released Wednesday by Bloomberg Politics showed Rubio with a hefty 10-point lead.
But the contest between Trump and his Democratic opponent, former Secretary of State Hillary Clinton, has continued to dominate the airwaves. And Rubio, who has haltingly supported Trump after losing the battle for the party's White House nomination, could need to outrun the top of the ticket by several points to win re-election.
Florida Chief Financial Officer Jeff Atwater said tying Rubio to Trump won't severely wound the senator's bid for a second term.
"Marco is well known in the state of Florida," Atwater said after the debate. "Marco will be re-elected because of the presence and the command of issues that have faced this country."
During the debate, Murphy blamed a budget move that Rubio spearheaded in the Senate for driving up premiums in the health-care marketplaces set up by the Affordable Care Act; Rubio said he was simply interested in barring taxpayer funds from being used to bail out insurance companies.
The two also clashed over whether to increase the minimum wage.
"Anybody's that's willing to work a full-time job in this country shouldn't be living in poverty," Murphy said.
But Rubio said he found it ironic that Murphy was trying to get an upper hand on working-class issues. Rubio said he was the son of working-class immigrants, while Murphy's father rose to become wealthy.
"You never had to worry a day in your life about where your next check is going to come from or how your next bill was going to be paid," Rubio said. "I have."
Foreign policy proved to be one of the focuses of the debate. The two candidates butted heads over President Barack Obama's diplomatic and economic overtures to Cuba, with Murphy saying increased opportunity for Cubans could be a better way to open the island than the five-decade-old embargo.
"Would we rather see our own cruise ships, Royal Caribbean and Carnival, there in Havana, or would we rather see Russian spy ships there?" Murphy asked.
That brought a withering reply from Rubio.
"Basically, an invasion of cruise ships is going to bring democracy to Cuba? It is not," he said.
One of the most bizarre moments of the evening came when the debate got bogged down in the weeds of the role of the Kurdish peshmerga in the fight against the self-proclaimed Islamic State, a terrorist group in Iraq and Syria that the U.S. has led a campaign against. Murphy rattled off several groups he said were involved in the related civil war in Syria, including the peshmerga.
"We also both know that Donald Trump probably can't name or identify any of those groups or their involvement," Murphy said.
"Can I just say, because he criticized someone for not knowing the facts about the region: Congressman, there are no peshmerga in Syria," Rubio responded "The peshmerga are Iraqi."
"And they are helping us fight," Murphy said.
"In Iraq, not in Syria," Rubio shot back.
Afterward, surrogates for Murphy split on their responses about whether Rubio or the congressman was right about the peshmerga. Democratic Congressman Ted Deutch declined to address the question directly, but U.S. Rep. Ruben Gallego, D-Ariz., said Rubio was incorrect.
"He may joke about it, but he was 100 percent wrong," Gallego said. "And anybody that actually understands the Middle East, anybody that's fought in the Middle East like I have, know that the peshmerga have crossed back and forth over that Syrian border, many times."
Murphy's campaign also blasted out a CNN story that indicated that in at least one battle in 2014, the peshmerga provided support in Syria to local Kurds.
But much of the focus on the specifics of militia movements in a faraway country might be sound and fury. Susan MacManus, a political science professor at the University of South Florida who was on hand for the debate, said Murphy's fate is largely out of his hands. Thus, the focus on Trump.
"Patrick Murphy's successes are very, very closely tied to Hillary Clinton," MacManus said. "If Hillary wins by a wide margin in Florida, Murphy will be the next U.S. senator."
Donald Trump and Kurdish militias little known among Florida voters dominated the second and final debate Wednesday between U.S. Sen. Marco Rubio, a Republican seeking re-election, and his Democratic challenger, Congressman Patrick Murphy.