The harder right the Republican Party turns, and the sharper left Democrats steer, the wider yawns a gap in the polarization of the American electorate.

Yet it may not be the two starkly diverging party platforms emerging from the national conventions — which candidates often run from, as opposed to running on — that divide voters this year so much as it is the party’s own nominees.

In the escalating rhetoric of Donald Trump and Hillary Clinton, experts see a divisiveness unseen in decades that only plays to a growing public perception among Republicans and Democrats that people of the opposite party are not only wrong on issues, but also close-minded and dishonest — possibly even immoral.

“The rhetoric is an extreme rhetoric this year — it’s inviting a no-vote instead of a yes-vote,” says Kathleen Hall Jamieson, director of the Annenberg Public Policy Center at the University of Pennsylvania.

“The problem with the way in which the campaign has structured itself this year is we are casting the opposing side as incompetent — as having ill intent,” she says. “You could go back to an era in which candidates said of the other candidate, ‘We disagree philosophically, but he is a good person.’” Trump and Clinton are “inviting their followers to believe that we are actually voting against something that is a menacing evil. And one can say on either side, ‘Well, objectively we are.’”

The widening political polarization of Americans is not only issue-oriented — it’s getting downright personal. For the first time in the Pew Research Center’s studies of American attitudes since 1992, majorities of people in both parties are voicing not only unfavorable, but also “very unfavorable,” views of the other party.

More than half of Democrats surveyed this year say the GOP makes them “afraid’’ — 49 percent of Republicans feel likewise. Most Democrats — 70 percent — say they consider Republicans more close-minded than other Americans. And about one-third see the other side as “immoral” or “less intelligent.” More than half of Republicans share that perception of close-mindedness on the other side, and close to half say Democrats are more immoral, “lazier” and “more dishonest.”

“In a way, we are flashing back to the polarization of 1968” — that Vietnam War era of national unrest — says Barbara A. Perry, professor of ethics and institutions at the University of Virginia’s Miller Center, which specializes in studies of the American presidency.

And the platforms which the parties stand ready to adopt in Cleveland next week and Philadelphia the following week are clear measures of that divide, she says.

“They represent the polarization and the extremes in our society,’’ Perry says. “These two platforms are reflective of the extreme wings of these parties. And since the more moderate parts of these parties have been stunned by the populism of Donald Trump and Bernie Sanders, it’s even more obvious now that what these platforms are reflecting are these two movements on the right and the left.’’

Convention delegates will vote on planks pitting one party against the other:

— Democrats seeing “much work to be done” on LGBT rights and promising “federal non-discrimination protections;” Republicans supporting the right of states and federal government not to recognize same-sex marriage.

— Republicans supporting a human-life amendment to the Constitution; Democrats protecting “reproductive health and rights around the globe.”

— Democrats saying undocumented immigrants “should be incorporated completely into our society through legal processes;’’ Republicans opposing “any form of amnesty’’ and supporting a full wall along the Mexican border.

— Republicans pledging to uphold the Second Amendment; Democrats seeking stronger gun controls.

— Democrats promising to revive the Equal Rights Amendment and secure equal pay for women and men; Republicans pledging to fight workplace discrimination.

— Democrats backing a $15-an-hour minimum wage, calling the current minimum “a starvation wage;” Republicans promising “job creation with economic growth.”

— Republicans intent on repealing Obamacare; Democrats promising universal health care and a “public option.”

— Democrats upholding voter rights and restoring all protections of the Voting Rights Act; Republicans supporting photo-IDs for voters at polling places.

— Republicans promising “domestic energy independence” and “reining in” the EPA’s regulations restricting greenhouse gas emissions; Democrats supporting caps on emissions, pledging the nation will run on clean energy by mid-century.

— Democrats vowing to fight “the greed and recklessness of Wall Street;” Republicans opposing the notion of “too big to fail” and Dodd-Frank regulations.

There’s a reason Sanders calls his party’s “the most progressive platform the Democratic Party ever has had.” He wrested key concessions in it before acceding to Clinton’s nomination, just as conservative and evangelical forces insisted on stances in the GOP platform that Trump might not instinctively have taken.

“What you’re seeing is, the Bernie Sanders wing of the party, what I’ll call the 1960s Great Society big government platform, come to fruition for the Democrats,” Perry says. “And what I see with the Republicans is sort of a warmed-over Reaganism… and what Trump has been talking about in the last few days, which is law and order.”

At the same time, history shows there’s nothing holding any nominee to every plank of a party’s platform

“For practical purposes, platforms are irrelevant,” Jamieson suggests. “The platforms serve to tell the also-ran candidates that their voice is still being heard.’’

It will be telling to follow Clinton’s campaign talk about the minimum wage moving forward, Jamieson says — Clinton has advocated a $12-an-hour floor. And, Jamieson notes, “reporters have enough trouble holding Trump accountable to Trump, much less having to hold him accountable to his party’s platform.”

The real “electoral calculus,” she suggests, is how the candidates counter one another on any issue — though at this stage, it’s a battle of character, not credo.

Clinton, standing this week at the old Illinois Capitol where Abraham Lincoln delivered his “house divided” speech, cast her opponent as unfit for the presidency — calling him “as divisive as any we have seen in our lifetimes.” Trump responded with trademark Twitter-talk: “Voters understand that Crooked Hillary’s negative ads are not true — just like her email lies and her other fraudulent activity.’’

If Americans are split over the tenets of the nation’s major parties and presumptive nominees and increasingly distrustful of the political opposition, the parties also are riven within their own ranks.

“At times it seems like the forces pulling us apart are stronger than the forces holding us together,’’ former President George W. Bush said this week.

He was speaking of the fault lines in American society exposed by the ambush on police officers in Dallas and police shootings in Minnesota and Louisiana. But he might as well have been addressing the election contest at hand: Neither the 43rd president, nor his father the 41st, nor brother Jeb Bush, who lost to Trump in the primaries, plans to attend his own party’s convention this year.