Nearly every poll about the 2016 presidential race shows Hillary Clinton scooping up about two of out every three Democratic primary voters and leading every possible Republican contender.

As a mainstream left-of-center Democrat, she would extend Obama's policy legacy, and in turn, help facilitate a generational ideological shift. At the same time, the bitter 2008 primary allows her to avoid being perceived as an Obama clone, so she can distance herself from any unpopular aspect of Obama's tenure.

As a woman president, she would be a historic first. She has as complete a resume as anyone could possibly have before becoming president, which makes any attack on her qualifications vulnerable to charges of a "glass ceiling" barring women from the presidency. No matter what conservatives claim about Benghazi, Hillary Clinton is beyond vetted.

So with Democrats entering into the 2016 race with the clear upper hand, why does it seem like the left is anxious to recruit a challenger? We keep hearing rumblings about Elizabeth Warren, Bernie Sanders, Howard Dean, and Martin O'Malley.


Because if Hillary becomes president by coronation, she doesn't owe anybody anything. And then, who knows what she might do?

In the same way that conservative activists live in fear that Republican picks for the Supreme Court have a tendency to "evolve" leftward on issues like abortion and gay rights once they are freed from the politics of the Senate confirmation process, progressive activists are perpetually anxious that Democratic presidents will drift rightward on issues like Social Security, welfare spending, and Wall Street regulation once surviving the gauntlet of presidential politics.

And the best, though by no means foolproof way, to prevent a Democratic president from embracing a "Nixon goes to China" moment is to pin the nominee down during the primary process.

Few believe Hillary is beatable in a Democratic primary. Instead, the hope is that a candidate making Hillary work to secure votes from her left flank will pressure Hillary to take clear pledges against Social Security cuts or rapid deficit reduction that she'll have a hard time breaking once in the Oval Office — especially if activists can plausibly claim that the pledges were intrinsic to her victory.

There is reason for progressive activists to cling to this hope. The big momentum killer for Hillary in the 2008 primary was when she tried in a debate to defend the New York governor's plan to extend drivers licenses to undocumented workers, while also refusing to outright support it. The two-step sparked a debate pile-on and ignited concerns of Hillary as an overly calculating politician. She may be inclined to bend over backwards to avoid a repeat performance, eschewing nuance for clear positions and giving progressives leverage to box her in as much as possible.

However, former Secretary of State Hillary Clinton starts the 2016 race with a deeper and broader amount of support than pro-Iraq-War-voting Senator Hillary Clinton did in the 2008 race. A primary challenge playing only to progressive activists may not be able to muster up more than 30 percent support in a two-way race, which wouldn't put much pressure on Hillary. She may be able to glide past attempts at extract pledges with rhetoric that allows her plenty of wiggle room in the future. The danger for progressives in having their dream agenda hitched to a sure loser is that the agenda may appear diminished once the primary is over.

But progressives may conclude a challenge is worth the risk to try to exert influence over a President Clinton, especially if there is little risk of preventing a President Clinton.

While the Tea Party-infused Republican primary scrum in 2012 forced Mitt Romney into embracing extremist rhetoric like "self-deportation" — which proved devastating in the general election — the bitter 2008 Democratic primary only made Barack Obama battle-hardened without forcing him into politically untenable positions. Similarly in 2016, there's little threat to Hillary's ultimate election to try to make her say "no Social Security cuts" during the primary.

Fortunately for Hillary, the Democratic left isn't as crazy as the Republican right.