Democratic presidential candidate Hillary Clinton tried to link her opponent, Sen. Bernie Sanders, to the Koch brothers by making a reference to an ad released by an organization associated with the Koch brothers during the debate on March 9. (The Washington Post)

Hillary Clinton went after Bernie Sanders on just about everything during the eighth Democratic presidential debate Wednesday night in Miami. Immigration. Health care. The auto bailout. There were hits and there were misses. But one strand of Clinton's broad strafing of Sanders made zero sense: that the Vermont senator is somehow a secret friend to Republicans and conservative major donors.

Here was Clinton on immigration:

In 2006, when Senator Sanders was running for the Senate from Vermont, he voted in the House with hard-line Republicans for indefinite detention for undocumented immigrants, and then he sided with those Republicans to stand with vigilantes known as Minute Men who were taking up outposts along the border to hunt down immigrants.

So I think when you were running for the Senate, you made it clear by your vote, Senator, that you were going to stand with the Republicans. When you got to the Senate in 2007, one of the first things you did was vote against Ted Kennedy's immigration reform which he'd been working on for years before you ever arrived.

And Clinton casting Sanders as in the pockets of Charles and David Koch:

I guess Senator Sanders, that the Koch brothers, as you said, are sensible with how they use their money. And I agree with you. They stand for things that I find abhorrent, that would be bad for our country, bad for our future.

But they did just put up a little video praising you for being the only Democrat who stood with the Republicans to try to eliminate the Export/Import Bank, which has helped hundreds and hundreds of companies here in Florida be able to export their goods and employ more Floridians. So from my perspective, you sided with the Koch brothers.

Here's the thing: No one — and I mean no one — thinks that Sanders is on the side of "hard-line Republicans" or that he of the millionaires-and-billionaires-are-ruining-our-politics riff thinks the Koch brothers are great and takes their side on, literally, anything.

The attack that works on Sanders — and Clinton has pursued this line, too — is that he is full of pie-in-the-sky proposals that sound good but are not based in anything close to reality. That Clinton believes in many of the same things Sanders espouses but has the added value of knowing how to move the levers of powers to actually get things done. That what Sanders says sounds good but simply cannot be done — and reflects a deep and dangerous naïveté about the political process.

But it's hard to see how anyone — Clinton supporter, Sanders supporter or undecided Democrat — would be convinced that Sanders is a liberal in name only or a fair-weather liberal. In the recently released Georgetown University School of Public Policy Bipartisan Index, Sanders ranked as the single least bipartisan senator in the chamber. The second least bipartisan? Ted Cruz. And no one on planet Earth would accuse Cruz of being a secret enabler of liberals.

At The Washington Post/Univision debate in Miami, Democratic presidential candidates Bernie Sanders and Hillary Clinton panned Donald Trump, vowed to reform immigration and sparred over their respective records. (Sarah Parnass/The Washington Post)

My guess is that Clinton's attack, strategically speaking, was an attempt to show how Sanders's quirkiness — he was the only Democrat to vote against the Export-Import Bank, for example — puts him outside the mainstream of Democratic thought. That his commitment is not to core Democratic principles but rather to his own vision and beliefs. And that such a politician represents a too-unpredictable variable to take a chance on in the 2016 presidential race.

I get it. I just don't think it will work. Sanders is a liberal's liberal. Attacking him as something short of that only hardens his support and makes Clinton look like she is all politics, all the time, and the facts be damned.