With the midterms over, political operatives and professional pundits are quickly turning their attention to the 2016 presidential election. Their interest, though, is unbalanced, focused on the wide-open Republican field. Many don’t expect a competitive Democratic primary. Will anyone even challenge Hillary Clinton? Some Democrats worry Clinton's supposed inevitability will come across as arrogance. “She's an enormously capable candidate and leader,” Massachusetts Governor Deval Patrick told CNN in May. “But I do worry about the inevitability thing, because I think it's off-putting to the average voter."

It is appearing more and more likely, however, that Clinton will face primary opponents. In fact, three potential candidates—Senator Bernie Sanders, former Senator Jim Webb and Maryland Governor Martin O’Malley—have all signaled they will seek the Democratic nomination.

Of the three potential candidates, Sanders seems most serious about running for president. The clearest sign came Tuesday when Tad Devine, a major Democratic consultant who worked closely with Al Gore, John Kerry, and Michael Dukakis, said that he would work with Sanders. “If he runs, I’m going to help him,” Devine told the Washington Post. “He is not only a longtime client but a friend. I believe he could deliver an enormously powerful message that the country is waiting to hear right now and do it in a way that succeeds.”

Sanders, who is a socialist, has been a vocal critic of President Obama and the Democratic Party for failing to go after Wall Street and being too close to big-money interests. He believes Clinton is no different, and this has made him consider a presidential run. On Saturday, he appeared on C-SPAN’s “Newsmakers” and talked about a potential campaign as well. "If there is not that support, I will not run,” he said. “I want to run a good campaign and a meaningful campaign and a winning campaign. If I can't do that, I'm not interested in running."

Ryan Lizza documents Sanders’s commitment to challenging the Democratic Party in a new piece for The New Yorker focusing on Clinton’s supposed inevitability. Lizza does not assess whether Clinton is actually inevitable. Instead, he describes how O’Malley and Webb, along with Sanders, are both positioning themselves for presidential campaigns. For instance, O’Malley spent time in Iowa campaigning for Democratic gubernatorial candidate Jack Hatch. Hatch lost by nearly 22 points, but O’Malley still used the campaign to introduce himself to Iowa voters. On Sunday, the Washington Post reported that O’Malley, whose term is up in January, sent 32 staffers to battleground states across the country during the midterms—another sign he is thinking about 2016.

Webb has done the least to prepare for a presidential run, but he is certainly flirting with the idea. “I do believe that I have the leadership and the experience and the sense of history and the kinds of ideas where I could lead this country,” he told Lizza. “We’re just going to go out and put things on the table in the next four or five months and see if people support us. And if it looks viable, then we’ll do it.” He travelled to New Hampshire in October to discuss his memoir, a chance to introduce himself to voters in the pivotal state.

All three of these campaigns are in their infancy but there’s a very good chance that at least one—and possibly several—of them will run. Each would likely challenge Clinton from the left on economic issues, attempting to tie her to Wall Street. Webb and Sanders have also been critical of her on foreign policy issues such as the interventions in Libya and Syria. In addition, there’s always the chance that Vice President Joe Biden or Senator Elizabeth Warren enter the race as well.

Can any of them derail Clinton as Obama did in 2008? Unlikely. Clinton is even better positioned now to ward off Democratic challengers than she was six years ago. But at the very least, a Sanders, O’Malley, or Webb campaign will force Clinton to defend her record and persuade primary voters that her agenda is best for the country. She may still be the inevitable candidate. But at least she’ll be prepared as well.