Hillary Clinton expected a coronation to the Democratic nomination, yet she’s been locked in a highly competitive primary that still isn’t over. But her biggest challenge isn’t a 74-year-old socialist from Vermont — it’s whoever wins the GOP nomination.

Out of the three remaining candidates, who would be the biggest threat to the Clinton machine? Each certainly brings his own strengths and weaknesses, but is there one candidate Hillary would least like to face, one who would give her a run for her money?

Sen. Ted Cruz is arguably the most conservative of the candidates and has the credentials to back it up. What’s more, he’s polished and far less gaffe-prone than GOP front-runner Donald Trump. Cruz would be the most appealing candidate to a broad base of conservatives and is the least likely to move to the middle on the issues — which could be his crutch in the general election.

Undoubtedly, Clinton will try to win over young women and millennials with her progressivism on social issues. She’ll paint the GOP nominee as extreme. Clinton will seek to paint Cruz as a hardliner on abortion and marriage, and to paint Trump as a neanderthal trying to take away women’s rights after his terrible gaffe on punishing women who receive abortions — a statement he has since walked back.

[lz_table title=”General Election Matchups” source=”NBC News/Wall Street Journal”]Hillary Clinton vs. Donald Trump

Clinton,50%
Trump,39%
|Hillary Clinton vs. Ted Cruz
Clinton,46%
Cruz,44%
|Hillary Clinton vs. John Kasich
Clinton,51%
Kasich,39%
[/lz_table]

Cruz has the Establishment backing in his fight against Trump, which bodes well for him in the general election, when the GOP machine will dump all of its resources into defeating Clinton. Cruz is the most likely candidate to face off with Trump if the convention is contested, which is why the Establishment has unenthusiastically thrown him its support.

Some within the Establishment have said they would’ve supported Ohio Gov. John Kasich, but he has almost no shot in the year of the “outsider.” But poll after poll of a general election matchup shows Kasich beating Clinton in November. Some believe that is because he has largely been left out of the vitriol of the GOP primary. Once he’s subjected to the Clinton machine’s attacks, that would drastically change.

A recent Washington Post/ABC News poll shows that Trump has the highest unfavorables of any candidate among all Americans, with 67 percent. Cruz follows with 53 percent and Kasich is the most palatable with 39 percent.

[lz_table title=”GOP Candidate Favorables” source=”Washington Post/ABC News”]Unfavorables among Public
Donald Trump,67%
Ted Cruz,53%
John Kasich,39%
|Favorability Among Public
Donald Trump,31%
Ted Cruz,36%
John Kasich,39%
|Favorability Among GOP Voters
Donald Trump,56%
Ted Cruz,58%
John Kasich,47%
|Unfavorables Among GOP Voters
Donald Trump,42%
Ted Cruz,38%
John Kasich,40%
[/lz_table]

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In the Democratic race, the numbers are similar to those of the Republicans — the front-runner has extremely high unfavorables with a majority of the electorate. Clinton’s unfavorables among Americans sit at 55 percent.

What’s more, Clinton’s poll numbers are terrible when it comes to honesty and trustworthiness. Many voters have a negative opinion of her according to polling from various outlets. The most recent one conducted in March, a Washington Post/ABC News poll, showed 57 percent of people think Clinton is dishonest and untrustworthy.

Somehow, Clinton and Trump have been able to weather every gaffe, controversy, and scandal and remain standing tall among their competitors — but it may not last forever when they’re the only two left. It may, in fact, come down to who is more likable, a bad sign for both Trump and Clinton.

Clinton knows what she gets with Cruz if he becomes the GOP nominee, but if Trump becomes the nominee he is a completely unpredictable wild card who could hurt Clinton — or, just as easily, incur self-inflicted wounds.

No matter which GOP candidate goes up against Clinton, that person will be going up against an embattled candidate looking to fight with all her might to assume the presidency — so he needs to be prepared. Polls also show GOP voters are far more enthusiastic about the race this year, meaning Clinton has an uphill battle, even before the battle begins.