The 2016 U.S. presidential race is not like elections past. It is not just a choice between right and left. The old borders are being redrawn by the parties, and by a restless, cranky electorate. No, the cleavage this year is different, and deeper. The line of demarcation is stark. It is no exaggeration to say that the choice in November is between sanity and insanity.

And there are no guarantees that voters will choose the candidate who, though she is far from perfect, at least spends most of her time in the reality-based community.

This election is about a credible candidate with flaws, versus a flawed candidate with no credibility. It's about a candidate with a mixed bag of policies, many deserving of criticism, versus a candidate whose nomination acceptance speech featured no concrete policies, other than pouring a couple of thousand miles of concrete to build a wall. It's between a candidate who can compromise, and who has at times compromised too much, versus one whose ego is so big, and whose inability to get over slights is so stunted, that he's still picking fights with Republicans he defeated in the primary.

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It's between a candidate who can offer the continuity of a third Obama term – all things considered, not a bad option – versus a candidate committed to sowing chaos, from ripping up treaties to ending alliances on a whim. One promises stability, the other promises a bumper crop of global supply of instability.

The good news is, Hillary Clinton is extremely well qualified to be president of the United States. The bad news is, she's less qualified to successfully run for the job. She's not comfortable enough to be a great retail politician. She has neither the folksy genius of her husband Bill, nor the egomaniacal magnetism of Donald Trump. She has spent a lifetime grinning and bearing and grinding her way to success, whereas Mr. Trump has spent a lifetime grinning and grinding other people down.

The good news is, she can stop Mr. Trump from reaching the White House. The bad news is, she's the only thing standing in his way. It's all on her. Her, and the American voter.

And so far, only about half of them, give or take a margin of error large enough to decide the election, are down with "I'm With Her."

Three months ago, what used to be known as the Republican establishment were convinced that the nomination of Mr. Trump would doom their party to a defeat of epic proportions. They foresaw the trifecta loss of the White House, Senate and House of Representatives. They may have overestimated the American public.

So far, the GOP base is solid for Trump. And more than a few people on the left hate Ms. Clinton so much – you heard them heckling at the Democratic convention, including during her acceptance speech – that they're contemplating not voting, or wasting a vote on a third party, or writing in Bernie Sanders' name. Or voting for Mr. Trump.

The race has come down to two candidates who do not have unified parties behind them – he only recently completed his hostile takeover of the GOP, while she does not yet have the full support of people who tried to take over the Democrats for Mr. Sanders.

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Given Mr. Trump's many flaws, the fact that most Republicans voted for someone other than him, and the way many prominent Republicans remain opposed to him, Ms. Clinton has a five-star opportunity to bring disaffected conservatives over to her side. But she also has a lot of disaffected Democrats to deal with – voters Mr. Trump would love to pick off, or at least convince to stay home in November.

If you listened to Ms. Clinton's acceptance speech, or consider whom she chose as her vice-presidential running mate, you saw these tensions at play. Because to win the election, she has to reach to the right, to attract soft conservatives who don't like Mr. Trump, while stretching to the left, and capturing Sanders supporters who don't like the modern Democratic Party.

Rhetorically, Ms. Clinton's speech presented the election not as a fight between Democrats and Republicans, but a contest between reasonable, level-headed Americans and unreasonable, intemperate Mr. Trump. She accused him of going negative on the U.S.A., talking it down and telling lies about how the great republic is not great. That's the accusation right-wing media figures and politicians have for years thrown at Mr. Obama. Ms. Clinton was speaking conservative to that audience.

She talked up the troops, the heroes of 9/11 and America's military strength. She nodded to American exceptionalism. She quoted Republican saint Ronald Reagan. And her mention of black Americans shot by the police was followed in the same breath by words of praise for America's brave men and women in blue. These were notes played to welcome conservatives who aren't warming to Mr. Trump's tune.

At the same time, however, a speech that was often rhetorically conservative was larded with policies further to the left than anything Mr. Obama or Mr. Clinton ever ran on. This was Ms. Clinton's genuflection to those who have been Feelin' the Bern, and who still wish the nominee were Bernie. She thanked him in her speech but more importantly, she allowed him to put his fingerprints all over her platform.

The former president Clinton devoted much of his political career to pulling the Democratic Party to the right. To win elections in the '90s, he had to. But if there is to be a future president Clinton, she will come into office on a platform pledged to undoing at least some of what her husband did. A higher minimum wage, free college tuition, a demand that American companies bring jobs back home and a distinct discomfort with free trade were all promised on Thursday night.

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The contest between Mr. Trump and Ms. Clinton shouldn't be a contest at all. She may not be the most capable Democratic campaigner, but outside of dystopian fiction, he would make the worst Republican president imaginable. Yet after a year of primary battles, they are the only candidates left. May the best woman win.