Hillary Clinton at a campaign stop in Nashua, N.H., on Tuesday. (C.J. Gunther/European Pressphoto Agency)

On both the left and right, the big loser in Monday’s Iowa caucuses was the political establishment. On the GOP side, the three establishment candidates — Jeb Bush, John Kasich and Chris Christie — won 6.5 percent of the vote . . . combined. Bush’s campaign and his super PAC, Right to Rise, together have spent $89.1 million so far — and about $14.9 million in Iowa alone. He won just 5,238 votes in the Hawkeye State, at a cost of about $2,674 per vote there.

Much of that money was spent attacking Marco Rubio. That strategy failed as well. In December, the Bloomberg Politics/Des Moines Register poll showed Rubio with just 10 percent support. Last night, he won 23 percent and barely missed passing Donald Trump to win second place. Rubio, who was elected to the Senate as an anti-establishment insurgent in the 2010 tea party wave and has one of the most consistently conservative voting records in the Senate, is now in a three-man race with Cruz and Trump. In the wake of Iowa, the “establishment lane” in the Republican race is effectively closed.

On the Democratic side, the establishment candidate, Hillary Clinton, effectively tied with Sen. Bernie Sanders (I-Vt.). Exactly one year ago, Clinton led Sanders 68 percent to 7 percent in the NBC News/Marist poll. That means she blew a 61-point lead. Worse, she has spent $90.2 million in the race so far. To put the Iowa vote in perspective, in 2008 Clinton lost the state to a young, attractive, articulate, rising political star; last night, she effectively tied with a 74-year-old disheveled socialist from Vermont. Not a good sign.

As my Post colleague Chris Cillizza correctly predicted, Clinton survived only because Sanders failed to make an issue of the scandal surrounding her emails. Big mistake. Sanders should have stolen a page from Donald Trump’s playbook and copied how Trump raised the issue of Ted Cruz’s Canadian birth. He did not have to argue Clinton did anything illegal; he simply had to say: “She’s got a problem, and she has to solve it. We can’t have a Democratic nominee who could be indicted before the election. She needs to get it resolved.” Most Democratic voters don’t care about the illegality of Clinton’s actions, but they do care about the impact on her electability.

Sanders will have to make the investigation an issue if he wants to win the nomination. He has an 18-point lead in New Hampshire and will almost certainly win the state. But after that, the field becomes much more favorable to Clinton. It’s not enough for Sanders to argue that he is more electable (though polls suggest he is). To win, he needs to raise doubts about Clinton’s electability in November by tapping into Democrats’ worst fear — that the FBI could actually find that she committed a crime.

The fact is there is no great love for Clinton among Democrats (just 22 percent say Clinton is “honest,” and just 40 percent say she is “likable”). Her husband was elected in 1992 for one simple reason: With the brief exception of Jimmy Carter, Democrats had been locked out of the White House since 1969. They were so desperate for power, they were willing to put up with Bill Clinton’s New Democrat triangulation — even if it meant welfare reform, free-trade agreements and a promised end to the “era of big government.” When Democrats were given a choice in 2008 between a return to Clinton-style triangulation or the real liberal in Barack Obama, they went for the real thing.

But Obama has been a disappointment for the Democratic left — a president who personally approved terrorist kill lists, eavesdropped on our calls and emails and failed to take on Wall Street or deliver universal single-payer health care. So now they have the same choice again: a return to Clinton-style triangulation or the real thing in Sanders. In their hearts, they feel the Bern.

Sanders appeals to the hearts of the Democratic base because he represents what Democrats wanted but did not get in Obama: a socialist who is not afraid to say he is one. But to close the deal, Sanders also has to appeal to their minds as well. He needs to make the case that if Democrats nominate Clinton, she could end up in the Big House instead of the White House.

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