Crucial political decisions often concern which bridges to cross and which to burn. Donald Trump’s dilemma is that he burns some bridges by the way he crosses others. His campaign depends on a low-probability event, and on his ability to cause this event without provoking a more-than-equal and opposite reaction.

Extrapolating from recent elections, the turnout of non-college educated whites this November would be expected to be 3 percent smaller as a portion of the total turnout than in 2012, and college educated whites a 1 percent larger portion. The core of Trump’s support consists of non-college educated whites, a cohort whose 2012 turnout was 60.4 percent. There is a low probability that Trump can motivate recent non-voters in this cohort to increase the turnout to 67 percent. There is, however, a high probability that the way he stimulates such people — still more insult oratory and fact-free “policy” expostulations — will cause other groups to recoil.

For the first time since at least 1952 — the first election for which ample data is available — Democrats probably will win a majority of voters with college degrees — a large and growing group (In 1952, 6.4 percent of Americans had completed college; today, about 33 percent have.) Consider, particularly, women with post-bachelor degrees. This fast-growing group — the percentages of women in law, medical and business schools’ enrollments are 48.7, 46.9 and 36.2, respectively — is already approximately 65 percent Democratic. Can Trump ignite a spike in the non-college white vote without causing a more-than-commensurate increase in the Democratic propensity of the college-educated?

Speaking of low-probability events, Trump’s literary interests were hidden until his vice presidential search took him to Charles Dickens’ “David Copperfield,” where he found Mike Pence, whose sometimes unctuous affect resembles Uriah Heep’s: So very ‘umble. The adjective “oleaginous” might have been invented to describe Pence’s performance with Trump on “60 Minutes”:

Being chosen by Trump is “very, very humbling.” Trump is “one of the best negotiators in the world” and will provide “broad-shouldered American strength.” Trump — “this good man” (what would a bad man look like to Pence?) — “is awed with the American people.”

Pence, a broad-spectrum social conservative saddened by our fallen world, can minister to the boastful adulterer and aspiring torturer who Pence thinks belongs in the bully pulpit. Actually, the sole benefit of Trump’s election would be in making the presidency’s sacerdotal role — the nation’s moral tutor — terminally ludicrous.

In May, Pence endorsed Ted Cruz but larded his endorsement with lavish praise of Trump, who excuses Pence for buckling “under tremendous pressure from establishment people.” In a year of novelties, now this one: A presidential candidate calls his running mate weak.

It will be interesting to see if Pence will defend his defensible opposition, as a congressman, to Medicare Part D, the prescription drug entitlement. When George W. Bush proposed this bit of “compassionate conservatism,” House Democrats voted 195-9 against it, deeming it insufficiently compassionate to seniors and excessively compassionate to pharmaceutical companies. Nineteen House Republicans, including Pence, voted against it, largely because this was the first major entitlement enacted without provision for funding. To give the Bush administration time to twist arms and dangle enticements, Republicans held open the floor vote for 2 hours and 51 minutes, twice as long as the previous longest House vote. It passed 216-215.

If pharmacology had been as potent in 1965 as it has become, prescription drugs might then have been included in Medicare. Today, will a pliable Pence amend his convictions and repent his resistance to this now immensely popular entitlement? Trump, Pence’s new lodestar, sees nothing amiss with the existing entitlement system and disparages those (remember the man who used to be Chris Christie?) who think trillions of dollars of unfunded liabilities are problematic.

Pence also has strongly favored free trade, including the North American Free Trade Agreement that Trump calls “the worst economic deal in the history of our country.” Never mind. In 1980, George H.W. Bush denounced Ronald Reagan’s “voodoo economics” until Reagan selected Bush as his running mate, whereupon Bush decided that it was very good voodoo economics. The malleable shall inherit the earth.

As Trump’s campaign manager, Paul Manafort, says, Trump “has changed the face of the Republican Party” just as Ronald Reagan did. Indeed. A snarl has replaced the sunny Southern California smile. Trump, himself a brand, has completed the rebranding of the Republican Party.

© 2016, Washington Post Writers Group