It seems almost too obvious to mention, but presidential candidates need a clear idea of why they want to be president. In the past few days, Democrats have heard that their still-undeclared frontrunner, Hillary Clinton, needs time to think about the question. Meanwhile, another undeclared hopeful, Elizabeth Warren, is thrilling liberal audiences with a forceful, point-by-point declaration of the principles that would guide her as president. The contrast is striking.

Clinton is offering Democrats her resume. Warren is offering them a plan.

In an interview with CNN on Monday, former president Bill Clinton said his wife needs time to "think through" what she might want to accomplish if elected to the White House. "We've reached a point in our life when we think you really shouldn't run for office if you don't have a clear idea of what you can do and a unique contribution you can make and you can outline that," Bill Clinton said. "Now that the book is done, she wants time to think about that and work through it."

The former president said "this has been the first free time" in years that his wife has had to think things over. But the Hillary vision problem is nothing new; the weak spot in her White House ambitions has always been offering voters a reason she should be president. That was the case in 2008, when she presented her experience as First Lady and senator -- not her vision -- as the main argument for her candidacy. Now it appears Clinton again views her experience, this time broadened to include a term as Secretary of State, as her prime qualification for the job.

In 2008, voters chose a far less experienced candidate who presented them with a more compelling vision. They could do the same in 2016.

The latest version of that compelling vision was on display last week in Warren's address to Netroots Nation, a yearly gathering of progressive activists. Warren has not said she will run for president, despite the chants of "Run, Liz run!" that nearly drowned out her speech. But Warren sketched out where she stands and how she would govern. The ideas she presented aren't new; they're progressive boilerplate. But they are a plan.

Warren gave the crowd her by-now familiar verdict that the American economic system is "rigged." She promised to fight against the rich and powerful. She pledged "a fight over economics, a fight over privilege, a fight over power," but most importantly, "a fight over values." ("Fight" is perhaps Warren's favorite word; she used it 40 times in a 15-minute speech.)

And then Warren presented a manifesto of sorts. "We believe that Wall Street needs stronger rules and tougher enforcement, and we're willing to fight for it," she began.

"We believe in science, and that means that we have a responsibility to protect this Earth."

"We believe that the Internet shouldn't be rigged to benefit big corporations, and that means real net neutrality."

"We believe that no one should work full-time and still live in poverty, and that means raising the minimum wage."

Warren went on to outline 11 points in all. She promised to fight for a "livable wage," to fight for relief from student debt, to fight to protect Social Security and Medicare, to fight for "equal pay for equal work," to fight for gay rights, to fight for immigration reform and to fight to overturn the Hobby Lobby decision and ensure that women "have a right to their bodies."

Of course the audience loved it. But Warren's message was more than just popular. It was a blessed relief for those activists in the more liberal corners of the Democratic Party who can't bear the idea of supporting an establishment candidate like Hillary Clinton who's gotten rich making speeches to Goldman Sachs. Warren's presence, even if she won't say she is running, is proof that there is a real alternative to Clinton.

But Warren offered the Netroots audience more than just a different face. She offered them an agenda. She didn't say she needed time to "think through" what needs to be done in this country. She didn't appear to wonder whether she should do anything at all.

Instead, Warren promised a spirited fight for specific things. Why wouldn't many Democrats prefer that to a candidate who's trying to figure out what she can contribute?