A new batch of Wikileaks emails highlighting Hillary Clinton's campaign were released last week and show that the first GOP candidate the Democrats saw as a threat wasn't Donald Trump but Marco Rubio.

At 43, the Florida Senator was the youngest Republican in a crowded field of 17 candidates and was seen by Clinton's advisers as similar to Obama, who bested Clinton in 2008 with his calls for a move away from the old guard politicians.

Wikileaks claims the emails come from the hacked account of campaign chairman John Podesta.

Neither Podesta or Clinton have denied their authenticity.

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Florida Senator Marco Rubio, the youngest of the GOP candidates, was seen as the early rival to Clinton - and someone who might best her the way Obama did

With his messages of change and youth, Clinton staffers noticed he sounded remarkably like Obama in his campaign rhetoric

'It’s interesting to compare/contrast with Obama 08,' a staffer wrote to Podesta, referring to Rubio saying, 'Yesterday is over, and we are never going back' in a campaign speech.

The staffer wondered if the statement was directed at Clinton, and emails bounced back and forth about whether to respond, but in the end they decided to let it lie.

'Don’t see reason to react here,' campaign communications director Jennifer Palmieri wrote, according to The Daily Beast.

'Agreed. Let them take it as an attack on Bush,' responded political consultant Mandy Grunwald.

Clinton staffers zeroed in on Rubio because they thought he would appeal to young voters - something Clinton wasn't doing

While the Clinton campaign may have decided not to hit back at what might have been a dig at Clinton, staffers clearly saw him as the one to watch.

'He gives a good speech, and sounded much more reasonable, populist and accessible than much of the rest of the GOP field,' wrote public relations maven Christina Reynolds, words that could have been used to describe the approach Obama took to beat Clinton.

'Felt more like an inspiring Democratic speech than a GOP candidate, outside of foreign policy, repealing Obamacare and choice. Lots of references to 'our generation’ (i.e. Him and younger voters) vs. 'their generation' (them being us, Jeb, his opponents, Washington).'

One staffer noted that Rubio's speeches were reminiscent of one Obama made when he said, 'This election is not just about what laws we will pass. It is a generational choice about what kind of country we will be.'

When Rubio tweeted that Clinton wanted to 'reset' policy with Cuba, the staff came up with a response tweet meant to make Rubio's foreign look out of date.

Emails to campaign chairman John Podesta showed the HRC staff wasn't particularly concerned about Trump - and even hoped he would get the nomination

'You've got it backwards: Engagement is a threat to the Castros, not a gift. Embargo hasn’t worked for 50+ years. -H' was sent out from Clinton's Twitter account the next day.

Luke Albee, an aide an advocate for Cuba engagement, wrote in the emails that Rubio's Cuba stance was at odds with his image as a fresh vision for the future: 'This policy [is] rooted in the Cold War,' he said.

But the real threat was lurking virtually unnoticed in the pack. Trump hardly figures at all in the early leaked emails, when he was seen as having scant shot at the White House, wrote Shane Harris in The Daily Beast.

But as the controversial businessman's popularity soared, the Clinton campaign seemed to take heart, feeling he would be an easier opponent than Rubio to trounce.

The staff was worried about Clinton's tenuous hold on young voters, who had gathered their support around Bernie Sanders, and felt Rubio would also be popular with them.

But Rubio dropped out of the race March 15, and Donald Trump, the unlikely dark horse, was rising quickly in the polls.

This not only didn't phase the Clinton staffers - many saw a Trump nomination as her best shot winning over young voters.

'Right now I am petrified that Hillary is almost totally dependent on Republicans nominating Trump,' The Hill columnist Brent Budowsky wrote to Podesta. '[S]he has huge endemic political weaknesses that she would be wise to rectify….even a clown like Ted Cruz would be an even money bet to beat and this scares the hell of out me….'