Jeb Bush is stepping up his attacks on presidential rival Marco RubioMarco Antonio RubioAna Navarro lashes out at Rubio for calling outrage over Trump's 'go back' tweet 'self righteous' US-Saudi Arabia policy needs a dose of 'realpolitik' Media cried wolf: Calling every Republican a racist lost its bite MORE (R-Fla.) for missing votes in the Senate, the day after he challenged him on the issue in the third Republican presidential debate.

“I’m not demonizing Marco Rubio to point out that he has the worst attendance record in the United States Senate,” Bush said on Fox News’ “Happening Now” on Thursday. “And it was the worst one prior to his campaign as well. That’s a problem.”

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“Pursuing your own ambitions at the expense of service of others is wrong.” 



The former Florida governor running for president said Rubio’s spotty attendance is emblematic of the broader dysfunction in Congress.



“A lot of people that can’t take time off unless they get a deduction in their pay — I mean, that’s the real world,” Bush said. “Are we creating an alternate universe in Washington, D.C.? That’s part of the problem.”



He said Rubio could fulfill his duty as a senator and run a presidential campaign at the same time, “but the simple fact is he’s not doing that.”



Bush has made Rubio’s attendance record a major line of attack, and said at Wednesday nights debate that the senator should resign from his seat.



Rubio responded to Bush in the debate by pointing out that his voting record is similar to other senators who have previously run for president.



He also said missing votes was a necessary sacrifice to prevent Democratic primary front-runner Hillary ClintonHillary Diane Rodham ClintonChelsea Clinton announces birth of third child Ukrainian officials and Giuliani are sharing back-channel campaign information: report A question for Robert Mueller MORE from winning the White House in 2016.

The rhetoric between the rival campaigns has been heating up in recent weeks.

Rubio has emerged as the biggest threat to Bush in the primary race, with establishment Republicans looking to him as a new standard-bearer if Bush continues to falter in the polls.