Speaking to reporters on his new campaign bus while driving through New Hampshire, Bush was pressed repeatedly about reports that Rubio misused a Republican Party credit card in Florida
"It's not my job to worry about that. It's your job," Bush said. "A candidate running for president that has a chance to be president will be thoroughly vetted."
Bush, in an apparent effort to look more transparent, pointed to the 33 years of tax returns and thousands of emails that he released this year.
"I'm probably the most vetted so far. My past has been discussed in all sorts of ways -- sometimes comfortable, sometimes not so," he continued. "And Marco and every other candidate who is a viable candidate will go through that same process. That's up to you guys, not me."
Rubio hit back on attacks of his financial history on Wednesday, describing them as inaccurate. "I only have one debt in the world, which is my mortgage on the home that me and my family live in in Miami," Rubio said on "Good Morning America," adding, "I obviously don't come from a wealthy family."
Tensions between the two candidates have escalated as Rubio has surged in the polls, while his former mentor, Bush, has fallen to the middle of the pack.
Bush continued to say Wednesday that Rubio lacks much of a legislative record and argued that he's done little to bring reform to the nation's capital.
"He hasn't changed the culture in Washington," Bush said, when asked whether Rubio has lived up to expectations since he rode the tea party wave into the Senate in 2010.
As he has in the past, Bush pointed out that Rubio, along with Ted Cruz and Rand Paul, have only sponsored a total of two bills that have actually become law.
"That's one path," Bush said. "The other path is a path of public service where you accomplish things and that's my lane. And I'm going to talk about my lane."
Pressed on whether he'd support Rubio should he become the nominee, Bush said, "Absolutely."
"I will support every person on the stage running against Hillary Clinton," he said. "I'll be the nominee, though."