Progressives have three words for anti-Trump conservatives: "Be with her."

It's a reference to Hillary Clinton's slogan, "I'm with her," and it may seem like a fair enough request. But what most progressives don't realize is how big of an ask this is to make of a conservative. Yes, GOP nominee Donald Trump's character and noxious rhetoric pose an unusual threat to our Republic. But it doesn't automatically follow that one should vote for Hillary.

Some writers have tried to explain why it's so difficult for conservatives to stomach voting for Hillary by imagining a world where the presidential nominee scenario is flipped. Slate's Seth Stevenson, for example, asked readers to "imagine a world where the wackadoo candidate is in the other party." The wackadoo Democratic nominee in his make-believe race is Sean Penn. Stevenson concludes (very rightly, in my view) that progressives would hold their noses and vote for Penn rather than a "normal" conservative like Rick Santorum or Ted Cruz.

But Santorum and Cruz don't really work as Clinton surrogates in this situation. They are both mostly reviled by the left because of their social extremism, and while Hillary has moved very far to the left, and essentially offered anti-Trump conservatives nothing to join her coalition, her history of triangulation and ideological pincers (witness her perfectly timed "evolution" on same-sex marriage, a question on which no one doubts Rick Santorum would probably literally die rather than "evolve") makes the parallel inappropriate.

But a perfect parallel does exist: Dick Cheney.

Hillary Clinton is to the right what Dick Cheney is to the left.

Imagine, if you will, that Cheney didn't have a history of heart attacks and was still as spry as Bernie Sanders (who is just one year younger, by the way). Imagine that BushWorld had sent Cheney instead of poor Jeb into the presidential race.

Rather than playing beta to Trump's alpha, the practiced debater easily humiliates Trump on the stage and uses that $100 million in super PAC money to carpet bomb the pretend-billionaire with effective attack ads when it could have mattered instead of wasting them on Marco Rubio. Cheney places second in New Hampshire, rallies the establishment in South Carolina, and wins easily in a three-way contest against Cruz and Trump.

So on the left, you have Sean Penn. On the right, Dick Cheney.

I think most progressives would still vote for Sean Penn.

Before you claim that the comparison isn't apt, really think about Hillary Clinton and Dick Cheney. Both have been in politics forever. Cheney was White House chief of staff under Gerald Ford, and like Clinton, he has been in and around the White House in some capacity for more than 20 years. In those years, both have racked up their fair share of scandals. Both Cheney and Clinton are hawks, who got into the president's head to push an ill-conceived foreign adventure in the Arab world.

If you're ever a bit puzzled why conservatives fixate so much on Clinton's family foundation, which rakes in money from giant corporations for reasons that still aren't clear, think back on the left's exasperation over Cheney's ties to Halliburton. The left surmised that helping the oil industry was part of Cheney's rationale for pushing the war in Iraq. Well, Hillary Clinton pushed her friend Sidney Blumenthal's business ventures in post-war Libya.

If you ever wonder why conservatives are so apoplectic over Hillary's email server, think back to the Plame affair, when Dick Cheney allegedly outed a CIA agent as retribution for political criticism. With Hillary, conservatives see the same pushing of political advantage at the expense of the law and of national security.

If you're ever unsure why conservatives are so hysterical over Benghazi, think back to the countless times when it was alleged that Cheney covered up important information about the wars in Afghanistan and Iraq.

The perceived defensiveness, the almost preternatural refusal of having sunlight shone on one's affairs, and to have accountability for what one does; in both cases, all of that adds to an overwhelming feeling — and, perhaps, a trail of evidence justifying that feeling — that, behind the genteel façade, there is a cold, calculating brain looking out only for its own interest, one that would do anything to benefit itself so long as it could get away with it.

So, progressives, if you'd have trouble voting for Dick Cheney over Sean Penn, imagine how conservatives feel about supporting Hillary Clinton over Donald Trump.