Recently, a representative from the Hillary Clinton camp delivered a message to Martin O'Malley, the former Maryland governor preparing to challenge Clinton for the 2016 Democratic nomination.

I have some good news and some bad news, the messenger said.

What's the good news? asked O'Malley.

The good news is we're taking you seriously, the messenger answered. And the bad news is … we're taking you seriously.

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The undertone of threat was unmistakable, but anyone who takes on Clintonworld has to expect that. And indeed, pro-O'Malley Democrats — there are some — are not at all surprised by the tone. "They are the most petty, vengeful people out there," says one Democrat of the Clinton organization. "They hold a grudge for decades. I don't think he [O'Malley] expected them to welcome him with a fruit basket."

And Clintonworld has reason to be concerned. Yes, Hillary's lead is huge, and yes, she is at this point the presumptive Democratic nominee. But there are already emerging signs that the coronation might not go as planned.

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It's early yet, but O'Malley's declaration last Sunday — "The presidency of the United States is not some crown to be passed between two families" — is probably the best line of the campaign so far. If you took a poll to gauge public opinion on that turn of phrase, approval would likely be very, very high.

"It was a very effective line," says another Democrat. "And it's the first time he's taken a swing — he's always deferred in the past."

No more. O'Malley is acting like a real candidate now, traveling, hiring staff and fashioning a message. Democratic insiders point to three factors that could help O'Malley turn a non-race into a race.

1) Even when she has the nomination race to herself, Clinton rarely rises above 60 percent with Democrats. (In the RealClearPolitics average of polls, she is currently at 59.6 percent.) "There is one-third to 40 percent of the Democratic electorate that wants a primary race," notes the second Democrat. "Even in a field where she doesn't have an opponent, Hillary doesn't get above 65 percent." The job of O'Malley, or any other Clinton challenger, is to connect with that 35 percent to 40 percent of Democrats who are hoping for a Clinton opponent.

2) The history of Democratic primary battles is that an insurgent almost always puts a scare into the sure-thing frontrunner. "You can go back decades," says the Democrat. "There has always been a moment in the Democratic primary in which the overwhelming, conventional, odds-on establishment favorite was vulnerable to an outsider challenge." While that is truer of some years than others, there is a pretty long list of insurgents — Howard Dean, Bill Bradley, Jerry Brown, and others — who created some nervous moments for the leading candidate. In 2008, of course, the outsider Barack Obama did a lot more than that. And the odds-on favorite he toppled then just happens to be the odds-on favorite now.

3) The press wants a primary. Republicans can complain that the media is in the tank for Hillary, but there seems little doubt that many voices in the press would like to see an actual contest for the Democratic nomination. The Boston Globe, for example, recently begged Sen. Elizabeth Warren to run. "Democrats would be making a big mistake if they let Hillary Clinton coast to the presidential nomination without real opposition," the paper editorialized. The fact that some key voices in the press won't take Warren's "no" for an answer is an indication the fourth estate would like a fight. And if Warren stays out, they'll talk up any other credible challenger.

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O'Malley is more than credible. He has the credentials of a two-term governor and the ability to position himself to the progressive Left of Clinton. On Wall Street, LGBT issues, immigration, trade — on those and more, O'Malley can credibly cast himself as more progressive than Hillary.

"Hillary and Bill Clinton have been thick as thieves with Wall Street," says a pro-O'Malley Democrat. "She was very close with the financial industry, and she depends on them for money." Years after the economic meltdown, many on the Left are still angry that none of the big Wall Street players was punished, and it hurts Clinton to be associated with those players. "This is a really, really, really big issue with progressives — that there was no accountability for Wall Street," says the Democrat.

The planets are aligning for a real Democratic race. That doesn't mean Clinton will lose (although anything can happen), but it does mean there will be no smooth, easy path to the crown.