Dean Heller is a 57-year-old Mormon, husband and father of four who — because he is a U.S. senator from Nevada (having won in 2012 by a paper-thin 46-45 percent margin), a state that Barack Obama carried twice, and because he is the only GOP senator running in 2018 in a state that Hillary Clinton carried — is commonly referred to as the most vulnerable Republican incumbent facing re-election. Because Heller represents one-half of the two-seat majority by which Republicans now control the U.S. Senate, his re-election matters greatly to Mitch McConnell, the senator from Kentucky who desperately wishes to remain Senate majority leader.

Seeing as the most recent USA Today/Suffolk University national poll showed that a dismal 12 percent of Americans support the Senate Republican plan to replace Obamacare and seeing as Nevada’s Republican governor, Brian Sandoval, with a 66 percent favorable job rating, maintains that a big reason the number of Nevada’s uninsured children has been cut in half since 2012 is that his was the first GOP state to embrace Medicaid expansion under Obamacare, it should not have shocked anyone, least of all the White House, that the embattled Heller joined Sandoval in publicly opposing the widely unpopular bill.

Let history note that neither Heller nor Donald Trump — who, as he admits, has personally known just about everybody important — never met Hymie Schorenstein, the legendary Brooklyn Democratic ”boss” who could regularly produce winning margins of up to 20-1 for Franklin D. Roosevelt. He is also credited with the Schorenstein rule, which, simply put, is the professional politician’s overriding preference for a strong and popular candidate to head the party’s ticket on Election Day. Schorenstein explained his rule to a judicial candidate he had picked to run on the Democratic ticket but who — even after he gratefully had made a generous contribution to the party — had seen no buttons, bumper stickers or billboards with his name on them and questioned Schorenstein’s strategy.

”Listen,” Schorenstein bluntly lectured, ”did you ever go down to the wharf to see the Staten Island Ferry come in? You ever watch it and look down in the water at all those chewing gum wrappers and the banana peels and the garbage? When the ferryboat comes into the wharf, automatically it pulls all the garbage in, too. The name of your ferryboat is Franklin D. Roosevelt. Stop worrying!”

On Election Day 2016, Trump was, for most Republicans running with him on the ticket he headed, no ferryboat. Of the 22 Republicans who won Senate seats in 2016, 18 of them — including John McCain in Arizona and Rob Portman in Ohio, who rescinded their endorsements of the presidential nominee — ran ahead of Trump, who had very short coattails.

Ronald Reagan, who carried 44 states and 49 states in consecutive landslide victories and was one helluva ”ferryboat,” admonished his loyal supporters, ”The person who agrees with you 80 percent of the time is a friend and an ally — not a 20 percent traitor.” President Trump obviously disagrees. America First Policies, a political nonprofit (which means it does not have to reveal donors) staffed entirely by Trump loyalists, launched a million-dollar scorched-earth campaign in Nevada against Dean Heller, accusing him of ”standing with Nancy Pelosi,” the House Democratic leader. In political terms, going after Heller is the equivalent of shooting your own wounded. Mitch McConnell and other GOP senators objected strenuously to the anti-Heller attack ads, which were eventually pulled down, but not before Republicans everywhere had read the unmistakable message: This president will be your ally off and on, not exactly the sort of guy — with a 38 percent favorable job rating in the Gallup Poll — you look to as your Election Day ferryboat.

To find out more about Mark Shields and read his past columns, visit the Creators Syndicate webpage at www.creators.com.