There's a lot of chatter about what Hillary Clinton's campaign will actually be about. But the truth is, coming up with a policy agenda is the easy part. The hard part is going to be persuading voters that that agenda can pass.

The Obama years have been, for liberals, a searing lesson in the limits of the presidency. Obama made huge progress on liberal goals when he had a Democratic majority from 2009-2010. Since then, his legislative agenda has been blocked. A president without a Congress can't make much change. And the next Democratic president isn't going to have a Democratic Congress. Population patterns and gerrymandering mean the House is safely under GOP control at least into the 2020s.

Now, with Republicans nearly certain to keep control of the House, the 2016 Democratic candidates are going to have to somehow convince voters that they not only have ideas, but they have a plausible plan for getting those ideas passed into law.

The New York Times reports that at the Watermark Silicon Valley Conference for Women, Clinton previewed her answer. It's not very good:

She spoke at length about bipartisanship and promoted her record of working with Republicans in Arkansas and as a senator from New York. Her objective, should she run for president, would be to end partisan gridlock, she told Ms. Swisher. "I’d like to bring people from right, left, red, blue, get them into a nice warm purple space where everybody is talking and where we’re actually trying to solve problems," Mrs. Clinton said.

And I'd like to ride a Google Bus to work in the morning. But it's not going to happen. I don't work at Google. And Hillary Clinton doesn't work in a political system where right, left, red and blue are going to meld into a warm purple.

One reason Clinton lost in 2008 was that many believed her too polarizing to elect. They were tired of the partisan wars, the bitter divisions. They wanted a president who seemed capable of bridging differences, not destined to deepen the divides. In his influential endorsement of Obama, "Goodbye to All That," Andrew Sullivan wrote:

Clinton will always be, in the minds of so many, the young woman who gave the commencement address at Wellesley, who sat in on the Nixon implosion and who once disdained baking cookies. For some, her husband will always be the draft dodger who smoked pot and wouldn’t admit it. And however hard she tries, there is nothing Hillary Clinton can do about it. She and Giuliani are conscripts in their generation’s war. To their respective sides, they are war heroes.

As the thinking went, Clinton was intrinsically polarizing. She couldn't end the war because she was part of the war. But Obama, as a political and generational outsider, could end the war. He clearly believed this too. But he was wrong. Obama made the war worse.

Obama has been the most polarizing president since the advent of polling. But before him, it was George W. Bush. And before Bush, it was Bill Clinton. Party polarization — and its result, partisan gridlock — is structural, not individual. Obama couldn't end it. Clinton certainly can't. The fundamental fact of American politics right now is that party polarization is natural, partisan behavior is rational and gridlock is the result.

Clinton is promising what Obama, Bush, and, well, Clinton promised before her — to make politics work by making it less polarized. But she's not going to make it less polarized. She's somehow going to have to make it work even though it is polarized.

In 2008, Clinton made a version of this point in response to Obama's challenge:

Now I could stand up here and say 'Let's just get everybody together, Let's get unified. The sky will open. The light will come down. Celestial choirs will be singing. And everyone will know we should do the right thing and the world will be perfect.' Maybe I've just lived a little long, but I have no illusions about how hard this is going to be. You are not going to wave a magic wand and have the special interests disappear.

When Clinton talks about "special interests," she presumably doesn't include the Republicans. But they're not going to disappear either, and nor is partisan gridlock. If her plan is to pretend otherwise and to try to persuade the electorate that the gridlock of the last few years is unique to this era, well, that's not a very good plan.